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GEOLOGY  AND  ORE  DEPOSITS 

OF  THE 

RANDSBURG  QUADRANGLE 
OF  CALIFORNIA 

BULLETIN  Na.  $5 


ISSUED  BY  THE 

CALIFORNIA  STATE  MINING  BUREAU 
FERRY  BUILDING,  SAN  FRANCISCO 


THE  LIBRARY  OF  THE 

UNIVERSITY  OF  CALIFORNIA 

DAVIS 


FRONTISPIECE. 


^'l 


HIGH  GRADE  SILVER  ORE.  From  6th  level,  California  Rand  Silver  Mine. 
Drusy  cavities  and  angular  schist  inclusions  with  the  schistosity  oriented 
at  random  are  characteristic  of  the  ore.     Natural  size. 


37841 


CALIFORNIA  STATE  MINING  BUREAU 

FERRY  RUrr.DTNG.  SAN  FR\NCIS(JO 
LLOYD  L.  ROOT  State  Mineralogist 

San  Francisco]  BULLETIN  No.  95  [March,  1925 


Geology  and  Ore  Deposits 


OF  THE 


Randsburg  Quadrangle 


CALIFORNIA 


By 
CARLTON  D.  HULTN,  Ph.  D. 

LIBRARY 

UNIVERSITY  OF  CALiFORNIA; 
DAVIS 


CALIFOKNIA  STATE  PRINTING  OFFICE 

JOHN  E.  KING,  State  Printer 

SACRAMENTO,    1925 

LIBRARY 

UNlVERSliY  OF  CALIFORNIA 
DAViS 


f\ 


CONTENTS. 


Page 

INTRODUCTION    H 

PART  I.      GENERAL.  GEOGRAPHY  AND  GEOLOGY 13 

Location    13 

Accessibility   Ip 

Literature   1^ 

Bibliography    15 

Topography     1^ 

The  Rand  Mountains 1^ 

Red   Mountain    1'^ 

Lava  Mountains    1^ 

El  Paso  Mountains 1^ 

Summit  Range 1^ 

Valleys     18 

Climate    1^ 

Vegetation 19 

Water  Supply 19 

Geology    20 

General  Outline 20 

Rocks  of  Archean  Age 21 

Johannesburg  Gneiss 21 

Petrology     21 

Origin     23 

Structure 23 

Rand   Schist 23 

Petrology     , 23 

Origin     26 

Structure     27 

Relation  of  Rand  Schist  to  Johannesburg  Gneiss 38 

Conditions  of  Metamorphism  of  Johannesburg  Gneiss 38 

Conditions  of  Metamorphism  of  Rand  Schist 39 

Age  of  Johannesburg  Gneiss  and  Rand  Schist 39 

Undifferentiated   Strata   of  Paleozoic  Age 31 

Litholog>'  and   Structure 31 

]Mode  of  Accumulation 33 

Age 33 

Atolia   Quartz    Monzonite— 33 

Petrology 3  4 

Relation  to  Adjacent  Formations 37 

After  Effects  of  the  Bathonthi'c  Invasion 38 

Correlation  of  the  Three  Areas  of  Quartz  Monzonite 3S 

Mechanics   of   Intrusion 39 

Age 1 42 

The  Rosamond  Series 42 

Lithologj'     43 

Weathering     45 

Structure  and  Thickness 45 

Relation  to  Adjacent  Formations 46 

Conditions  of  Accumulation 47 

Age  and  Correlation  with  Adjacent  Regions 47 

Rhyolite-Latite    Series,  of    Intrusives 48 

Petrology     49 

Effects  on  Intruded  Rocks 50 

Age 51 

Weathering     , 52 

Diabase-Basalt  Series  of  Intrusives 52 

Field   Relations   52 

Petrology     53 

Weathering 54 

Age 54 

Red  Mountain  Andesite 55 

Field  Relations    , 55 

Mechanics  of  Extrusion _ 56 

Petrology 57 

Structure  and  Thickness 58 

Age 58 


915S5 


6  CONTENTS. 

Page 

Black  Mountain  Basalt 58 

Field   Relations   58 

Petrology     60 

Age 60 

Alluvium    60 

Ancient    Gravels    61 

Other     Alluviums     61 

Structure 61 

The  Garlock  Fault I 62 

The   Lava   Mountains 64 

The   Rand  Mountains 64 

Geologic  History 65 

PART  II.      MINERAL   DEPOSITS 69 

General   Statement 69 

The  Tungsten   Deposits 70 

Field    Relations 70 

Minerals   of  the   Deposits 72 

Grade  of  the  Ores ; 74 

Ore  Textures  and  Paragenesis 74 

Nature  of  the  Solutions  Which  Deposited  the   Ores 76 

Possible  Structural  Control  of  the  Ore  Deposition 76 

Age  and  Genesis  of  the  Denosits 77 

Possible  Extension  of  the  Tungsten  Deposits 78 

The  Gold  Deposits    79 

Field  Relations 79 

Structure  of  the  Deposits 80 

Nature  of  the  Veins 83 

Mineralogy    83 

Ore  Textures  and  Paragenesis 84 

Oxidation  and  Enrichment 86 

Age  and  Genesis  of  the  Deposits 88 

Structural  Control  of  the  Ore  Deposition 88 

Future   Possibilities  of  Gold  Mining 91 

Tlie    Silver    Deposits 92 

Field    Relations    92 

Structure  of  the  Deposits 95 

Nature  of  the  Vein  Filling 97 

Mineralogy    97 

Grade  of  the  Ores 99 

Ore  Textures  and  Paragenesis 99 

Alteration   of  the  Wall  Rock 102 

Order  of  Formation  of .  tlie  Minerals 103 

Age  and  Genesis  of  the  Deposits 104 

Origin   of  the  Veins , 104 

Structural  Control  of  the  Ore  Deposition 105 

Possible  Extension   of  the  Deposits 105 

Conclusion     106 

PART  IIT.      HISTORY   OF   MINING    lOS 

PART  IV.      MINES  AND  PROSPECTS 110 

California   Rand    Silver    Mine , 110 

Northeast  Veins   112 

Footwall    Veins   112 

Shaft  Vein    112 

Antimony    Vein    112 

Alpha  Vein 113 

Williams  Vein   113 

North-South    Veins    , 114 

Blanck    Vein    114 

Frog    Vein    ■ 114 

Treasure  Box  Vein 114 

Rourke    Vein    115 

Jameson   Vein    115 

No.    3   Stope   , 115 

518    and    530    Veins    115 

Sill  Vein   116 

Harrell    Vein    116 

Cow  Trail  Vein 117 

Hughs   Vein    117 

Grady   Lease   Vein    , 117 

Grady  West  Vein 117 

Wliirk    Vein    118 

Unnamed    Vein    118 

Nosser    Vein    118 

Number  Six  Workings 118 


COXTENTS.  7 

Page 

l-*roduction   and   Costs   119 

Yellow  Aster  Mine   121 

Mine   Workings   122 

Orebodies     122 

Cost  and   Production   124 

Properties  of  the  Atolia  Mining  Company 125 

I'nion    Mine    125 

Amity   Mine    126 

Attilla    Mine    126 

Acaley    Mine    126 

Papoose    Mine    126 

Mahood  Mine 126 

Flat   Iron   Mine - 127 

Par    Mine    127 

Goldstone    Mine    127 

Rainstorm    Mine    127 

PrudiR'tion     127 

Other  Properties 128 

Baltic- 128 

Beehive 128 

Bekher   Extension     128 

Ben   Hur 129 

Ben    Hur   Extension    129 

Bevis  Divide 129 

Big  Four 129 

Big  Gold    130 

Big  Six    130 

Black  Hawk 130 

Bray    and    Bisbee.-                     131 

Bully   Boy 132 

Butte    132 

Chicken   Hawk 132 

Cima   Bimetallic 132 

Consolidated 132 

Coyote 133 

Cuve 134 

Flat  Tire 134 

Fox-   Lease ' 134 

Garford   Lease 135 

Hard   Tack    J 135 

Hummer . 135 

Julius    Shades    136 

Kelly  Rand   Extension 136 

King   So'omon 137 

Little    Butte    137 

Miniuhalia     137 

Mizpali  Montana 138 

Mizpah   Nevada   138 

Monarch  Rand 138 

Nancy  Hanks 139 

Navajo  and  Swastika 139 

Oney  Lease 139 

Operator  Divide 140 

Rand   Contact 140 

Rand   Mountain 140 

Randsburg  Associated  Mines,  Inc. ^ 140 

Silver  Basin 141 

Silver  Bell 141 

Silver   Giant 141 

Silver  Glance  Lease 142 

Silver  King 142 

Sliverton    ^ 143 

South  Rand    143 

St.   Lawrence  Rand    143 

Treasure   Hill    143 

White   Horse   Rand 144 

Other  Lode  Properties 144 

Placer  Deposits   144 

Atolia    'Spud    Patch'     145 

Huelsdonk  Placer 145 

Oro   Fino   Placer .- 147 

Summit  Placer  Gold  and  Rock  Company,  Inc. 148 

Other  Economic  Deposits 148 


ILLUSTRATIONS. 


rage 

Plate     1.     Geologic  Map  of  the  Randsburg  Quadrangle In  pocket 

Plate     2.     Underground  Workings  of  the  California  Rand  Silver  Mine  and 

Adjacent   Properties    In  pocket 

Plate     3.     Underground  "Workings  of  the  Properties  of  the  Atolia  Mining 

Company    In  pocket 

Plate     4.  Underground  Workings  of  the  Yellow  Aster  Mine In  pocket 

Plate     5.  High  Grade  Silver  Ore,  California  Rand  Silver  Mine Frontispiece 

Plate     6.  A.   Main  Street  of   Randsburg  Looking  West.     B.  Randsburg  and  the 

Yellow  Aster  Mine    16 

Plate     7.  A.   Hornblende-plagioclase  gneiss.      B.   Biotite-albite   schist 24 

Plate     8.  A.  Biotite-hornblende-albite  schist.    B.   Chloritic-actinolite-albite  schist  25 

Plate     It.  A.   Outcrop    of    Rand    Seliist    Northwest    of    Randsburg.      B.  Southern 

Front   of   the    Bl    Paso    Range 30 

Plate  10.  A  and  B.   Quartz  Monzonite 34 

Plate  11.  A.  Thin  Section  of  an  Orbicle.     B.  Quartz-epidote  Rock 36 

Plate  12.  A.   Orbicular  Quartz  Diorite.     B.  Weathering  in  the  Rosamond  Series.  41 

Plate  13.  A.  Rosamond    Sandstone.      B.   Rhyolite 48 

Plate  14.  A.  Rhyolite    with   "Vermicular    Intergrowth.      B.   Basalt 50 

Plate   15.  A.   Rhyolite   Dike.      P..   Red  Mountain   from  the  West 55 

Plate  16.  A  and  B.   Pyroxene    Andesite    from   Red   Mountain 58 

Plate   IT.  A  and  B.   Black  Mountain  Basalt 60 

Plate   IS.  A  and  B.  The    Garlock    Fault    Line 63 

Plate   19.  A  and  B.  Thin    Sections   of    Scheelite    Ore 74 

Plate  20.  A  and  B.   Scheelite   Ore   76 

Plate   21.  A.   Thin   Section   of  Gold-bearing  Vein  Matter.      B.   Gold   Ore  from  the 

Sunshine  Mine 86 

I'hilf   :;2.     A.    Stope   at   the   Top  of  the  Rand  Vertical  Vein,   Yellow  Aster  Mine. 

B.  The  'Silver  Camp'   from  the   East 92 

Plat<'   23.      A.   Vein    Matter.    6th    Level,    California    Rand    Silver    Mine.      B.  Vein 

Matter,    11th   Level,   California   Rand   Silver  Mine 96 

i^hitt'   L'4.      A.   Miargyritc  Filling  Cavities  in  Earlier  Quartz.     B.   Banding  of  Pyrite 

and  Finely  Crystalline   Quartz 100 

Plate   25.      A.   Silver  Ore,   Showing  General  Relations   of  the   Minerals.      B.   Miar- 

gyrite  Surrounding  and  Replacing  Stylotypite 101 

Plate   26.     A  and  B.   General  Relations  of  Minerals  of  the  Silver  Ore 102 

Plate   27.      A.   Silicilication     of     the     Schist     Wall     Rocks     of     the     Silver     Veins. 

B.   Alteration   of  Metallic   Silver  Minerals 103 

Plate  2  8.     Map  of  Mining  Claims  in  the  Vicinity  of  Randsburg In  pocket 

Plate   29.     A.  lleadframe  of  No.   2   Shaft  and  Mill  of  the   California  Rand  Silver 

Mine.     B.   New  and  Old  Shafts  of  the  Union  Mine  Near  Atolia 111 

Plate   30.      Map  of  Mining  Claims  in  the  Vicinity  of  Atolia In  pocket 

Plate   31.     A.   Dredge  Installation  on  the  Norden  Placer  Claims.     B.   Stebbins  Dry 

Concentrator  on  the  Property  of  the  Oro  Fino  Mining  Company 14  6 

Figure   1.     Sketch  Map  of  California  Showing  Location  of  Area  Covered  by  this 

Report   14 

Figure  2.     Orbicles  Whose  Appearance  Suggests  That  They  Once  Formed  a  Single 

Mass     36 

Figure  3.  Portion  of  the  Randsburg  Quadrangle  in  Which  the  Atolia'  Quartz 
Monzonite  Would  Outcrop  if-  the  Tertiary  and  Later  Deposits 
Were   Removed    40 

Figure   4.  Fault  System  of  the  Yellow  Aster  Mine 88 

Figure  5.  Hypothetical  Cross-section  of  the  Ore  Bodies  of  the  Yellow  Aster  Mine  90 

Figure  6.  Structural   Control  of  Mineralization  Along  a  Fracture 91 

l'"'iguri'   7.  Idealized  Section  Tlirough  Silver  Deposits 94 

Figure   S.  Flow  Sheet  of  the  California  Rand  Silver  Mill 120 


LETTER  OF  TRANSMITTAL. 


To  His  Excellency,  Honorable  Friend  \\yi.  Kichardson, 
Governor  of  the  State  of  California. 

Sir:  T  luive  tlic  lioiior  to  herewith  transmit  Bulletin  No.  95  of  the 
State  ^Mining  Bureau,  relating  to  the  geology  and  ore  deposits  of  the 
Randshurg  Quadrangle.  This  area,  consisting  of  some  243  square 
miles,  has  one  of  the  most  interesting  histories  of  any  mining  area 
in  the  State  of  California,  and  a  production  of  over  $37,000,000  in 
appruxiiiiately  thirty  years'  time. 

^lininiT  started  in  1895  as  a  gold  (•aiii[),  ami  ()\rr  .$15,000,000  was 
pi'ddurcil.  Diii-ing  the  World  War  period  it  came  into  pi-omiuenee  as 
a  producer  of  tungsten,  from  wliieli  ])et\veen  $10,000,000  and  $1-,- 
000,000  were  i)roduced;  and  in  1917.  the  famous  Hand  Silver  Mine 
was  discovered  and  the  production  in  silvei-  from  1917  to  1925  is  in 
excess  of  $10,000,000. 

This  I'.iilletiii  is  presented  to  tlie  puhlic  so  that  the  detailed  informa- 
tion on  the  geology  and  ore  deposits  will  aid  and  assist  in  a  better 
understanding  of  this  area. 

Respectfully  submitted. 

Lloyd  L.  Root, 

State  Mineralogist. 


INTRODUCTION. 


Perhaps  no  miiiiiijr  region  of  the  west  has  had  a  more  varied  or 
fortunate  career  than  has  the  re^iion  surroimdinfr  Randsburg.  Initially 
located  in  189o  as  a  jrold  camp,  <rold  was  the  chief  metallic  product 
until  the  high  costs  resulting'  fi-om  the  World  War  forced  most  of  the 
jrokl  ])roi)erties  to  cease  operations.  At  the  same  time  the  war  created 
a  demand  for  tungsten,  wliich  resulted  in  feverish  exploitation  of  the 
tun<rsten  deposits  known  to  exist  near  Atolia.  Following  the  war, 
when  the  high  costs  still  prohibited  the  operation  of  most  of  the  gold 
properties,  and  when  the  market  for  tungsten  had  practically  ceased 
to  exist,  the  Pittman  Act  was  passed  guaranteeing  the  price  of  domestic 
silver  at  $1.00  an  ounce.  Ami  it  was  at  this  time  that  the  bonanza 
silver  deposits  were  discovered. 

Accurate  statistics  concerning  the  metal  production  of  the  quad- 
rangle are  practically  impossible  to  obtain.  It  seems  certain,  however, 
that  the  gross  value  of  the  metal  produced  between  1895  and  1924  has 
exceeded  $35,000,000.  Of  this  amount  nearly  $30,000,000  has  been 
taken  from  three  properties,  namely  the'  YelloAV  Aster  Mine,  the  Cali- 
fornia Raiid  Silver  Mine  and  the  properties  of  the  Atolia  Mining 
Company. 

Of  tlie  total  value  of  metals  produced,  slightlv  in  excess  of  $10,000,000 
may  be  credited  to  the  silver  deposits,  from  $10,000,000  to  $12,000,000 
to  tungsten,  and  the  balance  of  from  $12,000,000  to  $15,000,000  to  gold. 

Despite  the  value  of  metals  ]u-oduced.  but  little  geological  work  had 
been  carried  on  in  the  Randsburg  ((uadrangle  previous  to  1923,  the 
report  of  I\lr.  F.  L.  IIes.s  of  the  United  States  Geological  Survey 
published  in  1910  comprising  practically  the  oidy  data  available  to 
the  public. 

Realizing  the  need  of  more  detailed  information,  the  State  Mineral- 
ogist in  the  spring  of  1923  made  special  arrangement  with  the  writer 
to  map  the  geology  of  the  (| uadrangle  and  to  make  a  detailed  study  of 
the  mineralization. 

The  field  work  on  which  this  report  is  based  was  done  during  the 
summer  of  1923,  slightly  in  excess  of  two  months  being  spent  in  the 
field.  The  region  was  again  visited  for  a  few  days  during  the  early 
part  of  January,  192-4. 

Since  August,  1923,  detailed  studies  have  been  made  in  the  Geological 
Laboratories  of  the  T University  of  California  of  the  materials  collected 
during  the  field  work.  These  studies  have  bef^n  largely  microscopic, 
special  attention  haviiiii  been  paid  to  the  examination  of  the  metallic 
ores  by  reflected  light. 

As  a  result  of  the  work  which  has  been  done,  the  writer  has  arrived 
at  entirely  new  conclusions  regarding  the  age  and  genesis  of  the  ore 
deposits  of  the  quadrangle,  as  well  as  having  obtained  much  new 
information  regarding  the  general  geology.  Several  of  the  observations 
which  have  been  made  have  an  important  bearing  on  fundamental 
geologic  processes. 

The  mine  owners  and  operators  of  the  district  have  cordially  extended 
every  possible  assistance  in  the  preparation  of  this  report.  With  only  a 
single  exception,  fortunately  of  minor  importance,  access  to  mines  and 


—  12  — 

prospects  as  well  as  detailed  information  was  cheerfully  given.  Oppor- 
tunity is  taken  at  this  time  to  extend  thanks  to  all  those  who  so  willingly 
gave  of  their  time  and  assistance. 

Special  thanks  are  due  to  Mr.  Kent  S.  Knowlton,  to  Mr.  T.  D.  Walsh, 
engineer  in  charge  of  the  California  Rand  Silver  Mine,  and  to  Mr. 
G.  C.  Taylor,  all  of  Randsburg. 

Thanks  are  also  due  to  Professor  R.  R.  Morse  of  the  Department  of 
Geology  of  the  University  of  California  for  helpful  discussions,  sugges- 
tions and  criticisms  extended  from  time  to  time  during  the  preparation 
of  this  report. 

C.  D.  H. 
Geological  Laboratories, 
University  of  California, 
May  9,  1924. 


I 


GEOLOGY  AND  ORE  DEPOSITS  Of  THE  RANDSBURG 
QUADRANGLE,  CALIEORNIA. 

By  Carlton  D.  Hulin. 
PART  I.    GENERAL  GEOGRAPHY  AND  GEOLOGY. 


I 


LOCATION. 

The  Raiidsbiirg  quadraiijile  is  in  the  northern  portion  of  the  Mojave 
Desert,  lyino-  partly  in  Kern  and  partly  in  San  Bernardino  connties, 
California.  The  quadrangle,  whose  position  is  indicated  on  the  accom- 
panying sketch  map  (figure  1),  is  a  rectangle  which  lies  between 
117°30'  and  117°45'  west  longitude  and  between  35°15'  and  35°30' 
north  latitude.  It  is  roughly  14^1  miles  from  east  to  west  and  17^ 
miles  from  north  to  south,  covering  an  area  of  243.29  square  miles.  The 
topography  of  the  quadrangle  was  mapped  in  1900  by  the  United  States 
Geological  Survey  on  a  scale  of  1  :  62,500.  The  culture  was  revised  in 
1911. 

The  only  towns  in  the  Ilandsl)urg  quadrangle  are  Randsburg,  Johan- 
nesburg, Atolia  and  the'  recent  silver  camp  wiiich  lies  along  the  railroad 
a  mile  and  half  southeast  of  pJohannesburg.  This  last,  which  is  some- 
what strung  out  as  mining  camps  are  prone  to  be,  is  known  progres- 
sively from  north  to  south  as  Inn  City,  Osdick  and  Hampton. 

Randsburg  is  the  largest  town  in  the  quadrangle,  having  a  population 
estimated  at  from  500  to  700.  The  combined  towns  of  the  silver  camp 
are  probably  next  in  size  with  several  hundred  inhabitants,  followed 
closely  by  Johannesburg.  Atolia  was  a  camp  of  some  importance  during 
the  recent  World  War,  but  following  the  close'  of  the  war  the  tungsten 
mines  ceased  operations  with  th(!  result  that  Atolia  now  possesses  but 
few  inhabitants. 

ACCESSIBILITY. 

Access  to  the  region  may  be  had  by  either  of  the  two  railroads  which 
enter  the  (juadrangle,  or  by  stage.  A  daily  train  is  operated  over  a 
branch  of  The  Atchison,  Topeka  and  Santa  Fe  Railroad  which  extends 
from  Johannesburg  south  to  the  main  line  at  Kramer,  28  miles  distant. 
The  Owenyo  Branch  of  the  Southern  Paeitie  passes  through  the  northern 
part  of  the  quadrangle.  Stages  from  Randsburg  connect  with  daily 
trains  on  this  line  at  Searles,  a  station  in  the  north-central  part  of 
the  quadrangle.  Daily  stages  also  operate  between  Randsburg  and 
Mojave,  a  distance  of  slightly  over  forty  miles. 

Hotel  accommodations  are  available  in  either  Randsburg  or  Johan- 
nesburg. 

LITERATURE. 

Due  to  the  mineral  deposits  of  the  quadrangle,  this  region  early 
attracted  the  attention  of  mining  men  of  the  country,  so  that  from  time 
to  time  various  articles  concerning  it  have  been  published.    These  have 


—  14  — 

for  the  most  part,  however,  confined  themselves  to  brief  descriptions 
of  the  economic  features. 

The  first  serious  attempt  to  describe  the'  geology  was  made  by 
F.  L.  Hess  in  1909.  Since  that  time  the  United  States  Geological 
Survey  has  had  geologists  in  the  region  from  time  to  time  but  as  yet 
no  further  reports  have  appeared.    More  recently  the  fossil  content  of 


1  i 

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-Ir--— 


Figure  1.     Sketch  map  of  California  showing  location  of  area  covered  by  this  report. 


certain  sedimentary  strata  in  nearby  portions  of  the  desert  has  attracted 
the  attention  of  palaeontologists. 

The'  folloAving  bibliography,  though  possibly  not  complete,  is  believed 
to  include  all  of  the  more  important  papers  which  have  been  published 
concerning  the  Eandsburg  quadrangle  or  immediately  adjacent  portions 
of  the  desert  province.  A  number  of  the  papers  listed  are  popular  or 
semi-popular  in  nature. 


—  15  — 

BIBLIOGRAPHY, 
C.   Ia   Baker— 

Notes  on  the  Later  Ceiiozoic  History  of  the  -Mojavo  Desert  Region.     T'niv.  of 

Calif.  Bull.  Dept.  Geol.  Vol.  G   (1011)    pp.  333-3S3. 
riiysiography  and  Structure  of  the  Western  El  Paso  Range,  and  the  Southern 
Sierra  Nevada.     Tniv.  of  Calif.     Bull.  Dcpt.  Geol.  Vol.  7  (1912)  pp.  117-142. 

Walter  W.  Bradley- 
loth  Rept.  of  the  State  Mineralogist,  1915-191G.     Calif.  State  Min.  Bureau,  pp. 
830-839. 

(1.  Chester  Brown — 

14th  Rept.  of  the  State  Mineralogist,  1913-1914.     Calif.  Stale  Min.  Bureau,  pj). 
483-4 84. 

J.  A.  Carpenter — • 

Th."  Kelly  Silver  Mine  at  Randsburg,  California.     Eng.  &  ^fin.  Jour.  Vol.  108 

(1!H9)     11]).   UM)  UVA.       (A    popular   aceount   of   the   mine). 
Shaft  Sinking  in  the  Randsburg  District.     Pac.  Min.  News  of  the  Eng.  &  Min. 
Jour.-Press  Vol.  2  (1923)  p.  2(il.     (An  account  of  the  mining  practice). 

S.  II.  Dolbear— 

The  Occurrence  of  Tungsten  in  the  Rand  District.     Eng.  &  Min.  Jour.  Vol.  90 
(1910)    pp.  904-905. 

II.  W.  Fairbanks- 
Red  Rock,  Goler  and  Summit  Mining  Districts.     12th  Ann.  Rept.  Calif.  State 
Min.   Bureau.     1893-94,  pp.  456-458. 

C.  II.  Fry— 

The  Story  of  Randsburg.  Pac.  :\Iin.  News  of  the  Eng.  &  Min.  Jour.-l'ress. 
A'ol.  1   (1922)  p.  101.      (A  popular  account  of  the  district). 

II.  E.  Gregory  and  L.  F.  Noble- 
Notes   on    a    Geological    Traverse    from    Mojave,    California,   to   the    Mouth    of 
the  San  Juan  River,  Utah.     Ainer.  Jour.  Sci.     A'ol.  5   (1923)   pp.  229-239. 

F.  L.  Hess— 

(Jold  Mining  in  tlic  Randsburg  Quadrangle,  California.  U.  S.  G.  S.  Bull.  430 
(1909)    pp.   23^7. 

J.  C.  Merriam — 

A    Collection    of    Mammalian    Remains    from    Tertiary    Beds    in    the    Mojave 

Desert.     Univ.  of  Calif.  Bull.  Dept.  Geol.  Vol.  G   (1911)    pp.  1G7-1G9. 
New    l'rotohipi)ine    Horse   from    Tertiary    Beds   (vn    the    Western    Border  of   the 

Mojave  Desert.  Univ.  of  Calif.  P.ull.  Dept.  Geol.  Vol.  7   (1912)   pp.  435-441. 
Tertiary  Mammalian  Faunas  of  the  Mojave  Desert.     Univ.  of  Calif.  Bull.  Dept. 

Geol.   A'ol.   11    (1920)    pp.  438-585. 

J.  N.  Nevius — 

Notes  on  the  Randsburg  Tungsten  District.  Min.  &  Eng.  World.  Vol.  45 
(191G)    pp.   7-S. 

R.  W.  I'ack— 

Reconnaissance  of  the  Bar.stow-Kramer  Region.  U.  S.  G.  S.  Bull.  514  (1914) 
pp.  141-154. 

A.  B.  Parsons — 

The  California  Rand  Silver  Mine.  Min.  &  Sci.  I'ress.  Vol.  123  (1921)  pp. 
UG7-4j75:  855-859.  Vol.  124  (1922)  pp.  11-17.  (A  semi-popular  account 
of  the  history,  geology,  and  the  mining  and  milling  methods). 

J.  E.  Spurr — 

Descriptive  Geology  of  Nevada  South  of  the  40th  Parallel  and  Adjacent  Por- 
tions of  California.     U.  S.  G.  S.  Bull.  208   (1903). 
Succession   and   Relation   of   Lavas   in    the   Great   Basin   Region.      Jour.    Geol. 
Vol.  8   (1900)    p.  636. 

W.    II.     StOlTUS — • 

Geology  of  the  Yellow  Aster  Mine.  Eng.  &  Min.  Jour.  Vol.  87  (1909)  pp. 
1277-12S0. 

W.  B.  Tucker— 

17th  Rept.  of  the  State  Mineralogist,  1920.     Calif.  State  Min.  Bureau,  p.  361. 


—  16 


TOPOGRAPHY. 


The  general  topographic  features  of  the  Randsburg  quadrangle  are 
not  dissimilar  to  those  which  characterize  the  Mojave  Desert  in  general. 
Irregular  mountain  ranges  are  the  rule  rather  than  tlie  strikingly 
parallel  ranges  of  the  region  to  the  north  and  east.     The  major  portion 


PLATE  6. 


A.    MAIN   STREET   OF'  RANDSBURG  LOOKING  WEST. 


B.     itA.\J>SBURG  AND  THE  YELLOW  ASTER  MINE. 

of  the  quadrangle  lies  at  rlcvations  between  3000  and  4000  feet.  The 
lowest  point  in  the  quadrangle,  at  the  west  end  of  the  valley  to  the 
north  of  the  Rand  jNIountains,  has  an  elevation  of  slightly  less  than 


—  17  — 

2350  feet,  while  the  hig-liest  point,  the  suiiiinit  of  Red  Mountain,  is 
5270  feet  above  sea  level. 

THE    RAND   MOUNTAINS. 

Sevel-al  distinct  units  may  be  roeognizcd  in  the  mountain  ranges 
pre.sent  in  tlie  quadrangle.  As  will  be  shown  later,  they  are  not  merelj^ 
topojzraphie  units  ])ut  are  physiographic  and  geologic  units  as  well. 

Among  these,  one  of  the  more  prominent  is  the  Rand  Mountains. 
Rising  near  the  center  of  the  cpiadrangle,  these  trend  to  the  south- 
westward,  passing  out  of  the  quadrangle  and  continuing  on  for  some 
fifteen  or  twenty  miles.  The  Rand  Mountains  reach  their  maximum 
elevation  in  Government  Peak  (4755  feet),  a  mile  and  a  half  southwest 
of  Randsburg,  gradually  decreasing  in  height  both  to  the  northeast  and 
southwest  from  this  point.  The  range  is  notictvibly  asyniinetrie  in 
form  and  possesses  a  straight  front.  The  north  slope  is  quite  steep 
and  rugged  throughout,  a  drop  in  elevation  of  some  1500  feet  occurring 
within  a  mile  and  a  half  to  two  miles.  The  south  slope  on  the  contrary, 
is  quite  gentle  and  regular  up  to  the  very  crest.  This  is  especially  true 
towards  the  western  edge  of  the  quadrangle  where  the  slope  is  quite 
even  and  registers  a  decrease  of  1400  feet  in  some  six  miles.  This 
southern  slope  is  quite  smooth  and  practically  undissected,  so  much  so 
that  when  viewed  from  a  few  miles  to  the  south,  the  presence  of  a 
mountain  range  is  not  apparent. 

A  few  miles  to  the  southwest  of  the  quadrangle  a  low  rounded  hill 
with  rather  steep  slopes,  stands  out  prominently  on  this  otherwise  even 
southern  slope  of  the  Rand  ]\[ouii1ains. 

RED  MOUNTAIN, 

Located  several  miles  to  the  east  and  southeast  of  Johannesburg, 
Red  Mountain  stands  out  as  a  prominent  landmark  visible  for  miles 
over  the  surrounding  desert  country.  Its  upper  slopes  are  extremely 
steep  and  rugged.  About  two-thirds  of  the  way  down  the  mountain, 
however,  the  slopes  flatten  out  and  become  rounded  though  somewhat 
deeply  dissected  by  canyons  arranged  radially  around  the  mountain. 
When  viewed  from  a  distance,  the  top  of  Red  Alountain  is  seen  to 
possess  a  semblance  of  a  flat  crest-line. 

LAVA  MOUNTAINS. 

The  Lava  Mountains  lie  to  the  north  and  northeast  of  Red  Mountain 
and  topographically  form  a  unit  witli  it,  though  the  two  are  separated 
by  a  low  divide.  The  Lava  ^Mountains  possess  extremely  rugged  slopes 
and  a  very  noticeable'  flat  summit.  This  flat  summit  has  locally  been 
cut  into  b}^  sharp  ravines  and  deep  canyons  and  is  nearly  everywhere 
covered  with  lava  boulders  of  all  sizes,  so  that  making  ones  way  across 
the  surface  is  an  arduous  task. 

The  northern  end  of  the  Lava  Moimtains  culminates  in  a  straight 
and  very  rugged  northward-facing  escarpment  which  overlooks  a  flat 
alluvium-filled  valley.  Several  miles  to  the  south  of  this  escarpment, 
the  range  has  been  dissected  by  a  series  of  deep  canyons  which  flow 
both  to  the'  northeast  and  to  the  west  from  either  side  of.  a  divide  in  the 
center  of  the  Lava  Mountains. 

2—37841 


—  18  — 

EL  PASO  MOUNTAINS. 

The  El  Paso  Mountains  are  located  across  the  valley  to  the  north 
from  the  Rand  ^Mountains.  They  have  a  general  trend  from  northeast 
to  southwest.  Only  a  small  portion  of  the  total  length  of  the  range  lies 
inside  the  boundaries  of  the  Randsburg  quadrangle.  The  range  ter- 
minates to  the  northeast  in  Laurel  ^Mountain,  just  west  of  Searles.  That 
portion  of  the  range  within  the  Randsburg  quadrangle  is  quite  narrow, 
varying  from  less  than  two  to  nearl}^  five  miles  across.  Both  faces  of 
the  range  are  exceedingly  steep  and  rugged  and  are  cut  by  many  small 
and  immature  ravines  and  canyons.  The  .sunnnit  of  the  range,  in  con- 
trast, though  locally  dissected,  appears  to  po.ssess  a  mature  and  rounded 
topography.  The  high  points  of  the  range,  Laurel  Mountain  and  the 
El  Paso  Peaks  are  quite  inconspicuous  when  observed  from  a  distance, 
merging  into  the  general  summit  line  of  the  range. 

SUMMIT   RANGE. 

The  region  between  the  El  Paso  Mountains  and'  the  northern  end  of 
the  Lava  INIountains  is  occupied  by  an  irregular  series  of  low  hills 
which  have  been  termed  collectively  the  Summit  Range.  The  Summit 
Range  possesses  no  definite  features  of  its  own  unless  it  might  be  said 
tliat  the  very  absence  of  definite  characteristics  is  such  a  feature. 

VALLEYS. 

The  most  noticeable  valley  in  the  region  and  one  which  undoubtedly 
owes  its  origin  to  faulting  is  that  which  lies  between  the  El  Paso 
Mountains  and  the  Rand  Mountains.  This  valley  which  is  some'  five 
miles  broad,  heads  in  a  somewhat  ill-defined  group  of  alluvium-covered 
hills  near  the  north-central  part  of  the  quadrangle.  It  extends  south- 
westward  some  eight  miles  from  the  edge  of  the  quadrangle  where  it 
culminates  in  a  sink  known  as  Cane  Lake  at  an  elevation  of  about  1900 
feet.  This  valley  is  deeply  filled  with  alluA'ium  on  the  north  side,  as 
is  shown  b}^  borings  which  have  gone  through  600  feet  of  gravels  before  ' 
reaching  solid  rock.  On  the  south  side,  however,  occasional  exposures 
of  the  underlying  schists  project  through  the  alluvium  at  distances  of 
from  one  to  two  miles  from  the  front  of  the  Rand  ]\Iountains. 

A  somewhat  poorly  defined  valley  which  extends  well  across  the 
quadrangle  is  found  to  the  south  of  Atolia  and  Red  Mountain.  The 
alluvium  in  this  valley  is  ]>robably  nowhere  of  great  thickness,  though 
the  thickness  undoubtedly  increases  greatly  to  the  eastward  where  at  a 
distance  of  from  one  to  two  miles  from  the  edge  of  the  quadrangle  the 
vallej^  merges  with  a  sink  known  as  Cuddeback  Lake. 

Another  allnvium-fiUed  valley  is  fouiul  to  the  north  of  the  Lava 
^lountains.  This  valley  heads  in  the  vicinity  of  Searles,  and  trends  off 
to  the  northeast,  emptj-ing  into  Searles  Lake,  fifteen  miles  distant. 

CLIMATE. 

The  climate  of  the  Randsburg  quadrangle  is  quite  arid.  The  summers 
are  long  and  hot,  with  only  occasional  thunder  showers.  Parching 
winds  are  common.  These  are  sometimes  accompanied  by  sand  storms. 
Daytime  temperatures  of  100  to  105  degrees  occur  throughout  most 
of  the  summer  in  Randsburg,  while  in  the  low  or  more  sheltered  por- 


' 


—  19  — 

tioiis  of  the  quadranple  the  temperature  runs  somewhat  higher.  The 
ui'jhts  are  cool  and  ])leasaiit  ho-wever. 

During  the  late  fall,  winter  and  early  spring  raw  gales  occur,  some- 
times accompanied  by  freezing  temperatures.  During  the  first  week 
of  January,  1924,  temperatures  as  low  as  10  degrees  Fahrenheit  were 
recorded,  while  small  ])atches  of  snow  lay  on  the  higher  mountains  for 
over  a  week. 

Only  a  few  inches  of  rain  falls  in  the  region  during  the  year  but 
this  largely  comes  down  during  short  storms  with  an  intensity  approach- 
ing that  of  a  cloudburst. 

VEGETATION. 

because  of  the  general  aridity  of  the  climate  and  of  the  long  hot 
summers,  vegetation  is  quite  scant.  What  little  vegetation  doe's  occur 
is  largely  confined  to  the  lower  portions  of  the'  region.  Greasewood  and 
sagebrush  occur  accompanied  by  a  inimber  of  types  of  cactus.  The  only 
tree  otl'ering  shade  is  the  yucca  or  "Joshua  tree."  This  plant  was  only 
observed  growing  in  areas  underlain  by  quartz-monzonite  or  feldspathic 
sandstones  of  the  Rosamond  Series. 

ElVorts  are  being  made  at  dry  farming  in  the  valley  to  the  east  of  Ked 
Jlountain  and  also  north  of  Laurel  Mountain.  Some  of  these  efforts 
appear  to  be  meeting  with  success. 

WATER  SUPPLY. 

All  of  the  Avater  used  for  domestic  purposes  in  the  towns  of  the 
quadrangle  and  at  the  various  mines  is  obtained  from  a  number  of 
dtH'i")  wells  in  the  area  north  of  Red  Mountain.  While  these  wells  all 
start  in  llie  Red  JMountain  andesite,  no  data  could  be  ol)tained  regard- 
ing tile  rocks  penetrated  by  them.  The  wat(M'  obtained  is  of  excellent 
<|uality. 

In  times  of  shortage,  water  is  hi-onglit  into  the  region  in  lank  cars 
on  the  Sjinta  Fe  Railroad  and  pumped  into  the  mains  of  the  water 
com]iany. 

Water  foi-  mining  and  milling  ]nirposes  is  obtained  from  (le(>p  wells 
belonging  to  the  Yellow  Aster  Mining  and  Milling  Company.  Tiiese' 
wells  are  located  just  otf  the  map  and  immediately  in  front  of  the 
steej)  sonthei-n  face  of  the  El  I'aso  Mountains  adjacent  to  the  Garlock 
Fault.  When  the  wells  were  first  sunk  some  twenty  years  ago  water 
was  obtained  from  a  depth  of  -i'^i)  feet.  Since  then  pumi)ing  has 
reduced  the  water  level  fifty  feet,  the  water  now  being  pumped  from 
a  depth  of  .')(){)  feet.     Bedroek  occurs  at  a  depth  of  (500  feet. 

North  of  the  Garlock  Fault  line  water  is  obtainable  in  many  places 
at  fairly  shallow  de})ths  in  the  quartz  monzonite,  though  never  in  great 
([uantity.  A  number  of  wells  have  been  sunk  in  the  region  about  Laurel 
Mountain,  fi-om  most  of  which  water  of  good  (piality  has  been  obtained. 
At  one  well  a  half  mile  soutlieast  of  the  Hummer  J\line,  water  of  a  very 
poor  quality  was  obtained  at  a  depth  of  about  twenty  feet.  At  the  time 
of  the  San  Francisco  earthquake  in  1906,  the  water, level  in  this  well 
is  said  to  have  dropped  materially. 

South  of  the  Garlock  Fault  the  occurrence  of  water  appears  to  be 
veiy  erratic.  At  Bedrock  Spring  in  the  northeastern  part  of  the  Lava 
Mountains  a  small  flow  of  water  of  excellent  quality  is  obtained  through- 


—  20  - 

out  the  year  from  surface  lavas.  In  the  valley  to  the  east  of  Red 
Mountain,  water  of  not  very  o;ood  quality  is  obtainable  from  depths  of 
several  hundred  feet  in  p-ravels.  (Rosamond  Series?)  This  water  is 
used  for  irrigation  purposes.  Water  from  greater  depth  is  said  to  be 
quite  poor  in  quality. 

The  flow  of  water  in.  the  various  mines  of  the  district  is  somewhat 
erratic  and  see'minply  is  dependent  on  the  presence  of  open  fractures 
antl  other  local  geologic  features.  Thus,  water  stands  in  the  Cima 
Bimetallic  shaft  Avhich  is  only  200  feet  deep  in  Rosamond  sandstones. 
The  Big  4  shaft,  less  than  a  mile  to  the  southeast  has  been  sunk  to  a 
depth  of  1100  feet  i]i  these  same  sandstones  and  has  made  practically 
no  water.  The  California  Rand  No.  2  shaft  is  making  rather  abundant 
water  on  the  14th  level,  much  of  it  coming  from  the'  shaft  vein.  The 
Bray  and  Bisbee  workings  are  making  about  400  gallons  per  day,  the 
water  coming  from  the  500  and  600  levels,  while  the  Pittsburu-  and 
Mt.  Shasta  shaft,  1000  feet  to  the  south  is  making  some  4000  gallons 
of  water  per  day.  Water  was  first  met  in  this  shaft  when  a  vein  was 
intersected  at  a  depth  of  550  feet  from  the  surface.  Water  stands  in 
the  sump  of  the  Navajo  (C4rady  No.  2')  shaft  at  a  depth  of  about  1100 
feet.  It  is  not  known  how  high  this  water  would  rise  if  it  were  not 
kept  down  by  bailing.  Water  stands  in  the  shaft  of  the  Union  No.  1 
Mine  at  Atolia  between  the  10th  and  11th  levels  or  at  a  depth  of  about 
650  feet  below  the  surface.  It  is  said  that  no  water  existed  in  the  Little 
Butte  mine  at  Randsburg  at  the  520  level  previous  to  the  San  Fran- 
cisco earthquake  in  1906.  Following  the  earth(piake  water  came  in 
and  now  stands  at  a  depth  of  500  feet  in  the  shaft  incline.  Most  of  the 
shafts  of  the  region  aside  from  those  mentioned,  are  dry. 

GEOLOGY. 

A  wide  variety  of  rock  types  occur  within  the  area  covered  by  the 
Randsburg  quadrangle.  Igneous,  sedimentary  and  metamorphic  rocks 
are  all  represented.  The  igneous  rocks  include  plutonic  and  shallow 
intrusive  bodies  as  well  as  surface  flows.  The  sedimentary  rocks  include 
l)oth  nuirine  and  continental  deposits.  The  metamorphic  rocks  which 
include  both  gneisses  and  schists  have  been  derived  from  both  igneous 
and  sedimentary  sources.  The  rocks  range  in  age  from  Archean  to 
Recent. 

GENERAL  OUTLINE. 

The  Rand  ^Mountains  are  composed  of  a  series  of  flat-lying  schists 
which  have  been  intruded  by  a  later  batholith  of  (puirtz  mon/.onite,  and 
by  two  much  later  series  of  shallow  dikes  having  the  composition  of 
diabase  and  rhyolite-latite  respectively.  The  quartz  monzonite  out- 
crops over  much  of  the  southern  portion  of  the  quadrangle. 

Just  north  of  the  center  of  the  quadrangle  a  series  of  gneisses  are 
exposed  which  are  older  than  the  schists  of  the  Rand  Mountains. 

The  El  Paso  IMountains  are  composed  of  a  series  of  steeply-dipping 
Paleozoic  marine  sediments  which  have  also  been  intruded  by  the 
quartz  monzonite.  Quartz  monzonite  also  occupies  the  northern  por- 
tion of  the  Lava^Iountains  and  presumably  underlies  all  of  the  valle.v 
to  the  north. 

Red  Mountain,  the  Lava  ^Mountains  and  a  portion  of  the  Summit 
Range  consist  of  Tertiary  sediments  of  continental  origin  which  are 
capped  by  later  flows  of  ande'sitic  lavas. 


—  21  — 

At  several  places  in  the  vieiiiity  of  Siinimit  Di^^iiijis,  late  Tertiary 
or  early  Quaternary  iiitrusives  of  basie  composition  cut  the  okler  rocks. 

The  several  valleys  interveninji'  between  the  mountain  ranges  are 
filled  with  alluvium  which  has  been  derived  for  the  most  part  within 
01-  not  far  distant  from  tlie  (luadrangle.  The  thickness  of  this  alluvium 
is  (luite  variable. 

Faulting  is  of  importance  in  the  region.  One  of  the  major  struc- 
tural lines  of  California  is  found  in  the  Garlock  Fault  which  passes 
across  tlic  north(M'n  part  of  the  (piadrangle.  A  series  of  older  faults 
are  also  known  along  the  north  fronts  of  the  Kand  .Mountains  and  the 
Lava  ^Mountains,  as  well  as  elsewhere  in  the'  region. 

Only  two  fossils  have  been  found  within  the  quadrangle.  These 
were  Init  poorly  preserved.  In  conse(iuence,  all  age  determinations 
have  been  based  on  seciuence  and  on  petrological  similarities  with  hori- 
zons of  known  age  in  other  parts  of  the  desert  province. 

ROCKS  OF   ARCHEAN   AGE. 

Within  the  limits  of  tlie  Kandsl)urg  quadrangle  two  groups  of  rocks 
are  recognized  which,  owing  to  their  degree  of  metamorphism  are  con- 
sidered to  be  of  Archean  age.  The  older  of  the.se  tw^o  groups,  which 
will  be  referred  to  here  as  the  Johannesburg  gneiss,  consists  essentially 
of  crystalline  limestone  and  rocks  possessing  a  gneissic  texture.  The 
second  group  for  which  the  name  Rand  schist  is  here  proposed,  is  as 
the  name  implies,  composed  predominantly  of  true  schists. 

JOHANNESBURG  GNEISS. 

Hocks  of  this  groui)  outcro])  at  oidy  two  localities  within  the  area 
mapped.  The  larger  of  the  two  masses  is  exposed  over  an  area  approxi- 
mately two  miles  in  length  by  a  half  mile  in  width,  the'  center  of  which 
lies  two  miles  due  north  of  the  town  of  Johannesburg.  To  the  north 
the  rocks  here  exposed,  become  covered  with  a  mantle  of  Tertiary  sedi- 
ments and  volcanics  and  Quaternary  alluvium,  while  to  the  south  they 
appear  to  be  in  fault  contact  vnth  the  Rand  Schist. 

In  the  second  locality,  a  small  broken  xenolith  or  series  of  xenoliths 
are  included  in  quartz  monzonite.  forming  a  zone  not  over  one  hundred 
feet  wide  and  prol)al)ly  less  than  one  thousand  feet  long  inclusive  of 
breaks.  This  zone  lies  just  east  of  and  roughly  parallel  to  the  main 
highway  one-half  mile  southeast  of  Randsburg. 

Petrology. 

A  variety  of  rock  types  are  to  be  found  within  these  two  masses.  The 
majority  of  them  are  gneisses.  In  no  case  do  they  show  a  development 
of  a  true  schistose  cleavage. 

The  most  characteristic  type  represented  may  be  termed  a  horn- 
blende'-plagioclase  gneiss.  Rocks  of  this  class  show  a  parallel  banding 
of  the  light  and  dark  constituents,  white  bands  composed  of  a  fuie 
granular  crj^stalline  aggregate  whose  component  minerals  are  usually 
.so  small  that  they  can  not  be  recognized  with  a  hand  lens  alternating 
with  equally  thick  black  bands  which  even  with  the  unaided  eye  can 
usually  be  seen  to  be  composed  largely  of  black  hornblende.  The  thick- 
ness of  these  bands  varies  from  a  thirty-second  of  an  inch  or  even  less 
up  to  more  than  one-fourth  inch.     In  addition,  large  and  well-formed 


—  22  — 

porphyroblasts  of  black  hornblende,  usually  more  or  less  equant,  may 
be?  scattered  through  the  rock  mass  apparently  more  or  less  mdependent 
of  the  parallel  structure.  The  banding-  is  sometimes  highly  contorted 
and  broken  by  fractures,  giving  the  effect  of  a  minute  'Appalachian 
structure.'  Parallel  cleavage,  if  present  at  all,  shows  only  the  crudest 
development. 

On  microscopical  examination  the  white  bands  are  found  to  be  composed  of  a  fine 
grained,  even  granular  aggregate  of  andcsine  and  quartz,  with  occasional  larger 
jiorphyroblasts  of  andosiue.  The  feldspar  is  usually  present  in  greater  quantity 
than  the  quartz,  while  many  of  the  smaller  feldspar  grains  are  untwinned,  the 
larger  ones  commonly  show  both  albite  and  pericline  twinning. 

The  dark  bauds  consist  predominantly  of  strongly  pleochroic,  coarsely  crystalline, 
brown  hornblende  iutergrown  with  small  rectangular  plates  or  aggregates  of  deep 
brown  biotite.  The  hornblende  crystals  are  fairly  well  formed  and  usually  the 
length  is  less  than  three  times  the  diameter.  The  biotite  appears  to  be  orientated 
at  random  while  the  hornblende  crystals  lie  with  their  long  axes  in  or  making 
only  slight  angles  with  the  gneissic  banding.  Rather  abundant  magnetite  in 
irregular  patches,  together  with  a  fine-grained  dark  substance,  presumably  graphitic 
in  nature,  occur  scattered  through  the  dark  layers.  Local  areas  of  indefinite  outline 
which  are  characterized  by  abundant  closely  spaced  small  colorless  crystals  of 
diopside  are  developed  apparently  at  random  in  both  the  white  and  dark  bands. 
Traces  of  calcite  and  small  crystals  of  apatite  constitute  the  only  other  minerals 
observed. 

Microscopically  the  sharp  boundaiw  between  the  white  and  black  bands  vanishes, 
the  minerals  characteristic  of  either  baud  being  irregularly  iutergrown  within  a 
limited  zone  which  is  free  from  any  trace  of  parting. 

In  the  field  varying  types  are  to  be  found,  from  rocks  composed 
largely  of  material  found  in  the  white  bands  with  only  a  minor  develop- 
ment of  the  ferromagnesian  minerals,  through  intermediate  types  con- 
taining- roughly  equal  development  of  the  white  and  black  bands,  to 
massive  holocrystalline  rocks  composed  as  far  as  can  be  told  with  the 
unaided  eve,  entirelv  of  coarsely  crystalline  black  hornblende.  This 
last  type  may  be  termed  a  hornblende  gneiss. 

Microscopically  the  hornblende  gneisses  are  found  to  be  composed  almost  wholly 
of  large  interlocking  crystals  of  hornblende  which  appear  to  be  oriented  at  random 
or  nearly  so.  The  hornblende  is  strongly  pleochroic  chiefly  in  shades  of  deep  reddish 
brown,  but  the  brown  color  may  grade  into  shades  of  light  green  within  the  same 
crystal.  The  hornblende  crystals  are  cut  and  surrounded  by  irregular  veinlets 
and  patches  of  magnetite.     Traces  of  plagioclase  are  the  only  remaining  mineral. 

Interbedded  with  these  varying  types  of  gneisses  there  occur  rather 
important  quantities  of  a  massive  and  quite  coarsely  crystalline  marble. 
The  beds  of  marble  are  from  a  foot  to  twenty  feet  in  thickness.  The 
rock  is  almo.st  snow  white  in  color  and  is  composed  of  practically  pure 
calcite,  although  locally  small  flakes  of  black  graphite  occur  scattered 
through  it. 

There  sometimes  occurs  intercolated  with  the  limestone  in  thin  layers 
a  light-colored  gneiss  which  may  be  hard  to  ditt'erentiate  from  the  lime- 
stone. This  gneiss  is  massive  and  usually  without  parallel  structure 
and  is  composed  of  scattered  porphyroblasts  of  actinolite,  augite  and 
light  brown  garnet  set  in  a  matrix  composed  of  fairly  large  interlock- 
ing grains  of  plagioclase   (albite  to  oligoclase). 

A  more  or  less  pure  quartzite  is  the  only  other  rock  type  to  be 
observed.  It  occurs  in  subordinate  amount  interbedded  with  the 
marbles  and  gneisses.  It  may  be  massive  or  coarsely  banded.  The 
massive  variety  is  composed  almost  wholly  of  pure"  quartz  though 


—  23  — 

rarely  a  feldspar  cleavage  face  is  to  be  seen.  A  relic  clastic  texture, 
composed  of  rounded  medium-sized  sand  grains  can  usually  be  made 
out  with  a  hand  lens.  With  an  increase  in  amount  of  the  impurities 
present  in  the  rock  a  banding  is  dovelopod,  ])eing  the  result  of  the 
formation  of  thin  layers  of  light  brown  mica  possessing  a  parallel 
orientation. 

Origin. 

The  pJohannesburg  gneiss  has  clearly  been  derived  from  a  series  of 
rocks  which  were  predominantly  if  not  entirely  sedimentary,  probably 
a  series  of  marine  sediments.  The  quartzites  are  the  metamorphosed 
equivalents  of  original  bedded  sandstone,  in  general  quite  pure  or 
nearly  so.  The  2narl)les  are  similarly  the  metamorphic  product  of 
slightly  carbonaceous  but  otherwise  pure  limestones.  The  derivation 
of  the  hornbleiide-plagioclase  gneiss  and  the  hornblende  gneiss  is 
slightly  more  obscure,  but  their  composition  and  the  fact  that  they 
occur  interbedded  with  other  i-ocks  which  were  originally  limestones 
and  sandstones  would  suggest  that  tliey  were  derived  from  ferruginous 
shales.  The  light-colored  actinolite-pyroxene-garnet-plagioclaise  gneiss 
which  occurs  in  places  with  the  crystalline  limestone  is  especially  sug- 
gestive of  a  metamorphosed  shale.  It  can  not  be  denied,  however,  that 
some  portion  of  these  rocks,  especially  the  hornblende  gneisses,  may 
have  been  derived  from  igneous  rocks. 

Structure. 

The  structure  of  the  gneisses  exposed  to  the  north  of  Johannesburg, 
aside  from  minor  crumpling  is  quite  simple.  The  beds  have  a  general 
east  and  west  strike  with  dips  to  the  north  of  from  forty  to  sixty 
degrees,  though  locally  the  attitude  may  differ  radically  from  the 
figures  given. 

The  thickness  is  unknown,  neither  the  top  nor  the  bottom  of  the 
group' being  exposed.  A  thickness  of  approximately  2500  feet  of  these 
gneisses  actualty  outcrop. 

THE  RAND  SCHIST. 

Rocks  of  this  group  compose  the  bulk  of  the  Rand  Mountains.  As 
mapped,  they  cover  an  irregular  area  whose  maximum  extent  is  about 
ten  miles  from  northeast  to  southwest  and  over  four  miles  from  north- 
west to  southeast.  An  occasional  outcrop  projecting  through  the  allu- 
vium to  the  northwest  of  the  Rand  ^Mountains  indicates  that  the  total 
extent  of  the  Rand  Schist  is  probably  much  greater  than  would  be' 
indicated  by  the  mapping. 

Petrology. 

Over  most  of  the  area  occupied  by  the  schists,  but  especially  in  that 
portion  lying  east  of  a  north  and  south  line  passing  through  Govern- 
ment Peak,  the  predominant  type  of  rock  represented  is  a  mica-albite' 
schist.  This  rock  shows  a  highly  developed  schistosity.  It  is  usually 
a  dark  silvery-gray  in  color,  but  where  weathered  may  be  stained 
by  yellowish-brown  iron  oxides  set  free'  by  the  decomposition  of  the 
biotite  and  other  ferromagnesian  minerals.  As  viewed  on  a  schistose 
cleavage  surface  the  rock  appears  to  be  composed  largely  of  micaceous 
minerals,  chiefly  a  golden-brown  biotite,  though  some  are  light  colored, 


—  24  — 

arranged  with  a  parallel  orientation.  It  is  these  micas  which  give  to 
the  rock  its  silvery  sheen.  When  vieAved  perpendienlar  to  the  cleavage 
however,  the  niicaceons  minerals  are  fonnd  to  be  subordinate,  the  pre- 
dominant minerals  being  lenticular  grains  of  feldspar  and  quartz, 
everywhere  separated  by  thin  micaceous  layers.  These  lenticular  grains 
are  so  oriented  that  the  short  axis  of  each  is  perpendicular  to  the 
schistosity.    The  feldspar  in  general  shows  no  twinning. 

Microscopically  the  mica-albite  schist  is  found  to  be  composed  predominantly  of 
anhedral  grains  of  albite  and  quartz,  the  former  being  either  without  twinning  or 
ver.v  poorly  twinned.  The  proportions  of  albite  and  quartz  vary  considerably.  The 
allntc  tends  to  form  larger  grains  than  the  other  constituents  and  characteristically 
acts  as  a  poikilitic  host  for  many  of  the  other  minerals.  Graphitic  material 
especially  is  to  be  found  included  within  the  albites.  Though  nearly  or  entirely 
absent  from  some  crystals,  in  others  the  graphite  becomes  so  abundant  as  to  make 
the  all)ite  appear  almost  black.  Stubby  crystals  of  apatite  in  minor  quantity  are 
also  conuiionly  observed  as  inclusions  in  the  albite.  In  addition  to  the  albite,  por- 
l)liyroblasts  of  oligoclase  showing  well  developed  albite  twinning  are  occasionally 
found. 

Surrounding  the  albite  and  quartz  grains  is  a  matrix  consisting  chiefl.v  of  light 
colored  micas,  in  general  a  light  brown  biotite,  possessing  a  noticeable  orientation 
parallel  to  the  schistosity  but  locally  curving  around  the  grains  of  albite  and  quartz. 
Small  quantities  of  actinolite  and  green  hornl)lende,  oriented  with  their  long  axes 
at  random  in  the  plane  of  schistosity,  irregular  patches  of  magnetite  in  minor 
quantity,  and  occasional  traces  of  chlorite  complete  the  mineral  composition.  As 
will  be  pointed  out  later,  the  hornblende  and  actinolite  ai-e  believed  to  indicate,  in 
part  at  least,  a  transition  towards  other  schist  types. 

Next  in  abundance  are  numerous  amphibole  schists.  These  are  only 
slightly  subordinate  in  quantity  to  the  mica-albite  schists.  They  reach 
their  maximum  development  along  the  north  face  of  the  Rand  jMoun- 
tains  from  Government  Peak  southwest  to  the  border  of  the  map,  but 
commonly  occur  in  some  quantity  in  all  portions  of  tlie  formation  inter- 
bedded  witli  the  mica-albite  schist. 

Many  of  the  schists  of  this  group  consist  of  i)ractically  pure  actin- 
olite. The  actinolite,  light  green  in  color,  occurs  in  radial  bunches  or 
groups  of  interlocking  crystals,  the  individual  prisms  being  up  to  an 
inch  or  more  in  length  and  so  oriented  that  their  long  axes  lie  in  or 
make  only  a  small  angle  with  the*plane  of  schistosity. 

A  closely  related  type  cotisists  largely  of  fine  needles  of  actinolite 
set  in  a  matrix  of  talc,  the  long  axes  of  both  minerals  lying  in  the  plane 
of  schistosity.  Locally  the  actinolite  may  disappear  leaving  beds  of 
practically  \nn'e  talc  which  may  be  up  to  two  or  three  feet  in  thickness. 
In  these  schists  hornblende  may  take  the  place  of  actinolite  althougli 
the  latter  mineral  is  by  far  the  more  common. 

The  types  just  described,  the  actinolite  schist,  actinolite-talc  schist, 
talc  schist  and  hornblende  schist,  are  regarded  as  extreme  types  in  a 
series,  and  are  to  be  found  only  in  comparative  minor  amount.  The 
other  extreme  of  the  series  referred  to  is  the  miea-albite  schist.  Between 
these  limiting  members  all  gradations  are  to  be  found.  The  composition 
of  the  major  portion  of  the  amphibole  schists  of  the  Rand  ]\Iountains 
would  fall  i-oughly  about  midwaj^  between  those  of  the  two  limiting 
extremes. 

An  average  type  of  amphibole  schist  then  would  be  from  light  to 
dark  green  in  color  and  would  possess  a  well-developed  schistosity. 
As  viewed  on  the  schistose  cleavage,  the  rock  would  seem  to  b  composed 
of  a  fine  felt-like  intergrowth  of  amphiboles  (in  the  vast  majority  of 


PLATE   7. 


.'  •-  "fr^ 


Q 


A.  HORNBLEXDE-P  I^  A  G  I  O  C  I.  A  S  E  GNEISS.  H  =  hornblende  ; 
Br— fine  grained  hiotite  ;  Q  =  fine  g-ranular  aggregate  of  quartz  and 
plagioclase.       30   dia.   Ordinary   light. 


r>.    BIOTITE-ALBITE  SCHIST.      A  =  albite  ;   B  =  biotite  ;  Q  =  Quartz. 

54  dia.     X  nicols. 


37841 — facing  p.  24. 


PLATE    S. 


A.  BIOTITE-HORNBLENDE-ALBITE  SCHIST.  From  the  ^th  level 
of  the  California  Rand  Silver  Mine.  A  ^  albite  ;  B  —  biotite ; 
H  =  hornblende  ;    M  =  magnetite.       30   dia.       Ordinary   light. 


B.    CHLORITIC-A  CTINOIjIT  E-ALBITE     SCHIST.        A  r-  albite  ; 
C  =:  chlorite  ;    prismatic   mineral    is   aetinolite.       50    dia.   X   nicols. 


37S41 — facing  p.  2.'.. 


—  25  — 

eases  aetinolito^  and  small  quantities  of  micas.  Such  a  surface  possesses 
a  soft  sheeu  due  to  the  many  minute  crystal  faces  in  it.  When  viewed 
across  the  cleavao-e,  numerous  lenticular  feldspars  are  seen,  flattened 
parallel  to  the  schistosity,  with  the  flat  felty  layers  of  araphiboles  tend- 
iiipr  to  curve  around  them.  In  some  cases  the  feldspars  are  few  and 
minute,  and  the  ami)hiholes  very  small,  when  the  rock  louks  not  unlike 
a  jrreen  slate.  In  the  amphibole  schists  however,  there  is  a  strong  ten- 
dency for  these  lenticular  feldspars  to  become  enlar<ied,  in  which  case 
they  may  be  called  'augen'  and  the  term  anii)hil)olo-albite  augen-schist 
becomes  ai)plicable  to  t!ie  rock. 

Microscopically  these  augen  are  found  to  bo  auliedral  albite  ftrains  clouded  with 
poikilitic  inclusions,  as  graphitic  material,  fine  needles  of  actinolite  and  short 
prisms  of  apatite.  These  albite  porphyroblasts  are  surrounded  by  a  matrix  of  fine 
oriented  actinolite  needles.  Frequently  these  needles  pierce  the  grains  of  albite. 
In  some  cases  traces  of  chlorite  are  present,  while  almost  always  occasional  small 
crystals   of  diopside   arc  to   be   found. 

Quite  commonly  the  cloudy  albite  porphyrol)lasts  have  suffered  later  enlargement, 
a  ring  of  clear  albite  being  deposited  around  the  cloudy  kernel.  In  these,  prisms  of 
actinolite  may  project  through  the  ring  of  clear  albite,  perpendicular  to  the  outer 
surface,  usually  entering  tlie  inner  kernel  of  cloudy  albite  for  a  short  distance. 

An  especially  interest inu  ty})e  of  schist  occurs  a  short  distance'  south- 
Avest  of  the  Bully  B03'  Mine.  This  schist  consists  of  large  thin  plates 
of  light-gray  to  light-green  zoisite  set  in  a  matrix  composed  of  greenish- 
black  serpentine,  small  crystals  of  albite  and  flakes  of  muscovite. 
Individual  zoisite  crystals  may  be  as  much  as  an  inch  in  length,  a  half- 
inch  wide  and  an  eightli  of  an  inch  in  tliickness.  Schistosity  is  only 
jioorly  develo]ied  in  the  rock. 

Scattered  through  the  schists  at  various  horizons  there  occur  occa- 
sional small  flattened  lentils  or  nodules  composed  chiefly  of  a  green 
chrome  mica.  These  lentils  vary  from  one-fourth  of  an  inch  i\\)  to  an 
inch  in  thickness,  the  diameters  usually  being  three  or  four  times  the 
thickness.  They  are  easily  separated  from  the  surrounding  schist  and 
commonly  weather  out  and  remain  on  the  surface. 

Under  the  microscope  this  mica  was  found  to  be  colorless  in  thin  flakes.  Thicker 
flakes  Iiowever  were  light  a]>i)Ie-gr(M'n  in  color  and  slightly  pleochroic.  The  mica  is 
probabl.v  closely  related  to  fuchsite  and  mariposite,  and  possiI)ly  intermediate  between 
them.  The  indices  of  refraction  were  intermediate  between  those  of  these  two 
minerals,  wliile  in  different  flakes  2V  varied  from  0°  to  40°.  Dispersion  of  the 
optic  axes  was  very  strong   (r>v).     The  character  of  the  mineral  was  negative. 

Quartzites  and  limestones  occur  throughout  the  series  interbedded 
witli  the  mica-albite  schist  and  the  amphibole  schists.  They  very  in 
thickness  from  a  foot  or  possibly  less  to  over  ten  feet.  They  form  con- 
tinuous beds,  lensing  out  in  all  directions,  at  times  only  a  few  hundred 
feet  in  length ;  at  other  times  traceable  for  over  a  quarter  of  a  mile. 

The  quartzites  vary  greatly  in  purity.  In  many  cases  they  are 
massive  and  consist  essentially  of  pure  quartz  in  w^hich,  with  a  hand 
lens,  a  relic  texture  consisting  of  rounded  sand  grains  may  be  observed. 
In  other  cases  a  coarse  parallel  structure  is  developed  as  the  result  of 
thin  layers  of  light  brown  mica  which  ])arallel  the  schistosity  of  the 
adjoining  rocks.  The  (juartzites  are  usually  white,  pinkish  or  faint 
brown  in  color,  although  in  certain  cases  they  are  stained  black  Avith 
oxides  of  manganese. 


—  26  — 

The  limestones  are  white  to  lip'ht  sjray  in  color  and  appear  to  be 
slightly  carbonaceons  but  otherwise  fairly  pure.  Quite  contrary  to 
what  might  be  expected,  these  limestones  have  been  but  little  effected 
by  recrystallization,  their  texture  being  aphanitic  as  observed  with  a 
hand  lens.  Microscopically  they  show  some  development  of  diopside 
and  plagioelase  (oligoelase).  Limestones  are  generally  considered  to 
be  e"xtremely  susceptible  to  metamorphism,  but  here,  interbedded  with 
rocks  which  have  been  complete^  recrystallized,  they  appear  to  have 
been  one  of  the  most  resistant  types. 

The  only  remaining  type  of  rock  found  in  the  Rand  schist  is  a  green- 
stone-schist, quite  different  in  nature  from  the  previously  described 
types.  A  number  of  exposures  of  these  greenstone-schists  are  to  be 
found  along  the  north  flank  of  the  Rand  Mountains  west  of  Government 
Peak.  This  rock,  although  completely  recrystallized,  is  practically 
massive  with  only  traces  of  a  schistose  texture.  It  is  dark  green  in 
color  and  moderately  tine  grained.  In  the  field  it  was  observed  that 
this  rock  was  not  bedded  as  were  the  other  types.  It  occurs  in  small 
irregular  and  isolated  masses  which  quite  commonly  cut  across  the 
bedding  of  the  other  tj^^es  of  schists. 

Microscopically,  its  composition  was  found  to  be  quite  simple,  consisting  of 
rounded  grains  of  albite  set  in  a  matrix  of  light  green  hornblende  crystals.  The 
crystals  of  hornblende  Avere  oriented  in  all  directions.  Many  of  the  smaller 
crystals  were  included  in  the  albite  grains.     No  relic  texture  was  to  be  seen. 

Origin. 

The  massive  nature  of  the  greenstone-schist,  its  composition,  and  its 
habit  of  cutting  across  the  bedding  planes  of  the  other  schists  all  denote 
that  it  was  originally  an  intrusive  igneous  rock,  now  completely  recrys- 
tallized. The  lack  of  any  relic  textures  and  the  small  extent  of  the 
areal  exposures  would  tend  to  indicate  that  it  was  a  shallow-type 
intrusion,  with  a  tine-grained  or  glassy  texture,  rather  than  a  deep- 
seated  type.  Had  it  been  a  coarsely-crystalline  igneous  rock  formed 
under  the  influence  of  high  pressures,  it  seems  probable  that  it  Avould 
have  remained  stable  enough  to  have  preserved  traces  of  its  original 
texture  during  the  later  period  of  metamorphism. 

Of  the  remaining  rocks,  the  limestone  is  clearly  a  sediment  which 
has  been  but  little  changed  since  its  deposition,  while  the  quartzites 
are  just  as  clearly  derived  from  more  or  less  pure  and  well-sorted 
sandstones. 

The  composition  of  the  mica-albite  schist,  the  lack  of  relic  textures 
in  it,  and  the  fact  that  it  occurs  inter])edded  with  rocks  originally 
deposited  as  sandstones  and  limestones,  all  indicate  that  it  was  originally 
a  fine-grained  clay  shale.  The  nature  of  these  three  original  sediments, 
sandstone,  shale  and  limestone,  their  purity  and  the  character  of  their 
bedding  as  well  as  their  areal  extent  and  their  thickness  all  lead  to 
the  belief  that  they  represent  a  former  series  of  marine  sediments. 

The  origin  of  the  amphibole  schists  appears  to  offer  no  difficulties. 
Pure  actinolite  schists  occur  sharply  interbedded  with  normal  mica- 
albite  schists,  indicating  sudden  changes  of  short  duration  from  the 
normal  sedimentary  sequence.  The  beds  laid  dovn\  during  such  periods 
are  interbedded  as  are  normal  sediments;  they  show  no  relic  textures 
but  are  complete!}'  recrystallized  and  schistose,  showing  an  original 


—  21  — 

material  highly  susceptible  to  metamorphism.  In  the  majority  of  cases, 
howevoi'.  the  composition  of  the  ainplii1inl(>  schists  suggests  an  admix- 
ture of  a  basic  material  ^vith  the  normal  shales.  The'  only  explanation 
which  will  fit  all  the  facts  is  that  of  basic  volcanic  tuffs  interbedded 
with  or  mixed  Avith  normal  sediments.  In  times  of  intense  volcanic 
activity,  bods  of  nearly  pure  tuff  would  be  dojiosited,  noAV  observed 
as  aetinolite  or  talc  schists.  During  periods  of  lesser  activity  the  tutfs 
would  become  mixed  with  shales,  either  by  contemporaneous  deposition, 
or  through  mixing  as  the  result  of  the  action  of  water  currents  in  the 
basin  of  depositioii.  Such  mixtures  we  now  find  as  amphibole-albite 
schists.  And  in  times  of  volcanic  (piiescence  we  obtain  the  normal  sedi- 
ments interbedded  with  the  other  types.  The  concentration  of  the 
amphibole  schists  in  the  central  part  of  the  Hand  Mountains,  with  a 
general  feathering  out  tOAvard  tlie  east,  together  Avith  the  finding  of 
metamorphosed  intrusive  igneous  rocks  again  in  the  central  portion  of 
the  range  Avould  suggest  possibilities  as  to  the  location  of  the  former 
igneous  vents. 

Structure. 

Perhaps  the  most  striking  feature  of  the  Band  schists  is  the  con- 
cordance throughout  betAA'een  the  schistosity  and  the  original  bedding 
inherent  in  the  roeks  from  which  the  schists  were  derived.  Where  the 
schists  consist  solely  of  mica-albite  schists  or  of  amphibole  schists  the 
original  bedding  is  difficult  of  perception.  But  Avherever  a  bed  of 
limestone  or  of  quartzite  appears,  such  beds  or  contacts  are  alAA^ays 
parallel  to  the  schistosity. 

The  schists  Avhile  usually  almost  flat-lying  are  not  stricth'  horizontal 
but  show  broad  open  folds  and  a  regional  dip  over  most  of  the  area  at 
low  angles  to  the  south  or  southeast.  The  dips  on  the  flanlvs  of  the 
folds  seldom  exceed  fifteen  degrees  Avhile  the  regional  dip  is  much  less. 
The  formation  of  these  open  folds  appears  to  be  entirely  subsequent  to 
the  metamorphism. 

In  the  region  to  the  north  of  Johannesburg  the  beds  are  in  general 
flat-lying,  but  approaching  the  area  occupied  by  the  Johannesburg 
gneiss  a  rather  sharp  fold  appears,  so  that  on  the  contact  with  the 
gneiss  the  beds  posses.s  a  northAvard  dip  of  about  sixty  degrees. 

Near  the  contacts  Avith  the  Atolia  quartz  monzonite  intrusive, 
especially  those  Avdth  the  small  stock-like  mass  lying  just  south  of  Rands- 
burg,  the  schists  may  be  found  to  stand  in  any  attitude.  Local  blocks 
may  cA^en  be  found  to  stand  vertical.  Tliis  is  probably  the  result  of  local 
faulting  in  connection  Avith  the  batliolithic  invasion. 

Due  to  faulting  in  the  Rand  Mountains  no  exact  statement  can  be 
made  concerning  the  total  thickness  of  the  Rand  schists.  The  north 
front  of  the  mountains  shows  schist  exposures  through  a  A^ertical  dis- 
tance of  over  1800  feet.  AlloAving  for  a  low  southerly  dip,  the  total 
thickness  exposed  Avould  be  greater  than  this  figure,  providing  that  no 
alloAvanee  be  made  for  duplication  of  strata  through  faulting.  A 
number  of  hurried  trips  across  the  range  at  various  points  has  con- 
vinced the  Avriter  that  no  great  duplication  of  beds  occurs,  so  that  it 
seems  probable  that  between  1500  and  2000  feet  of  strata  are  actually 
exposed,  the  true  value  probably  being  closest  to  the  higher  figure. 


—  28  — 

Relations   Between   the   Johannesburg   Gneiss  and  the    Rand   Schist. 

The  relationship  existing  l)et\veen  the  Johannesburg  gneiss  and  the 
Rand  sehist  is  believed,  from  petrologieal  evidence,  to  be  one  of  uncon- 
formity, the  Johannesburg  gneiss  being  the  older  and  separated  from 
the  Rand  schist  by  an  intervening  period  of  metamorphism. 

The  exact  relations  existing  between  the  two  groups  can  not  be 
directly  determined  in  the  field,  but  they  are  l)elieved  to  be  in  fault 
contact.  As  mapped,  and  as  seen  in  the  field,  the  Johannesburg  gneiss 
appears  to  overlie  the  Rand  schist,  the  bedding  in  the  two  groups 
having  about  the  same  attitudes.  The  contact  is  everywhere  covered 
with  talus  and  alluvium  and  can  nowhere  be  located  more  accurately 
than  within  from  twenty  to  fifty  feet.  Within  this  zone  the  rocks 
change  abruptly  from  schists  to  gneisses  so  that  no  possibility  of  a 
gradation  exists.  The  mapping  indicates  that  the  contact  dips  to  the 
north  at  an  angle  of  about  sixty  degrees. 

It  is  inconceivable  that  the  series  of  gneisses  can  actually  be  younger 
and  actually  overlie  the  schLsts.  The  gneisses  represent  rock  tj'pes 
which  have  suffered  from  the  most  intense  metamorphic  processes/ 
while  the  schists  have  suffered  from  much  less  intensive  action. - 

The  limestones  of  the  Johannesburg  group,  as  has  been  pointed  out, 
are  coarsely  cry.stalline.  Their  bituminous  matter  has  been  changed 
to  graphite.  Whereas  the  limestones  of  the  Rand  series  are  micro- 
crystalline  and  show  only  a  slight  development  of  new  minerals. 

The  position  of  the  xenolith  of  gneiss  im])edded  in  quartz  monzonite 
southeast  of  Randsburg  is  such  that  it  c-ould  be  easily  explained  a^ 
having  been  lifted  up  from  lower  horizons  by  an  intrusive  magma,  but 
its  position  would  be  very  difficult  to  explain  on  the  hypothesis  of  its 
haying  sunk  from  a  higher  elevation. 

The  structural  conditions  are  such  that  the  possibility  of  an  over- 
turned fold  in  the  region  north  of  Johannesburg  can  also  be  ruled  out. 

The  only  remaining  po.ssibility  is  tliat  the  contact  represents  a  .strong 
reverse  fault,  possibly  a  bedding  fault,  the  older  Johannesburg  gneiss 
overriding  the  younger  Rand  schist.  The  obscurity  of  the  contact 
would  be  in  agreement  with  tliis  view. 

Supporting  the  possibility  also  are  evidences  of  faulting  observed 
close  to  the  line  of  the  contact.  In  three  shallow  prospect  shafts,  sunk 
in  the  schists  and  located  from  twenty  to  two  hundred  feet  from  the 
contact,  strong  faults  were  observed,  having  about  the  same  strike  as 
the  contact  and  dipping  steeply  to  the  north.  In  the  shaft  closest  to 
the  contact  a  brecciated  fault  zone  six  feet  wide  is  exposed,  possessing 
strong  walls  and  dipping  sixty  degrees  to  the  north. 

Conditions  of  Metamorphism  of  the  Johannesburg  Gneiss. 

The  massive  gneissic  textures  developed,  together  with  the  utter 
absence?  of  any  evidence  of  pneumatolysis,  indicate  that  the  recrystalli- 
zation  of  these  rocks  occurred  chiefly  as  the  result  of  ordinary  dynamic 
metamorphism,  whereby  intense  pressures  which  approached  a  hydro- 
static condition,  probably  aided  by  high  temperatures  and  solutions, 
were  the  active  agents.     The  fact  that  gneisses  were  formed  instead  of 

'  According  to  Grubenmann"s  sclieme  of  classification  they  would  be  formed  in  the 
upper  part  of  the  deep  or  "kata"  zone  of  metamorphism.  Dr.  U.  Grubenmann — Die 
Kristallinen    Schiefer. 

=  They  would  be  formed  in  the  upper  part  of  Grubenmann's  middle  or  "meso"  zone 
of  metamorphism. 


—  29  — 

schists  is  suggestive  of  the  intensity  of  the  metamorphie  action.  The 
pffects  of  lateral  stresses  are  shown  l)y  tlic'  contoi-tions  sometimes  seen  in 
the  gneissic  banding. 


Conditions  of  Metamorphism  of  the  Rand  Schist. 

The  most  noticeable  feature  of  the  Raiul  schist  is  tlie  concordance 
which  exists  everywhere  between  the  flat-lving  schistositv  and  the 
bedding.  The  slight  jimount  of  folding  which  has  effected  these  schists, 
occniM'ed  subse(|nent  to  tiie  metam()r])hism.  Ilenee  the  schistositv  must 
have  been  developed  hori/ontally  and  the  pressures  involved  were 
vertical.  The  effects  of  lateral  compression  are  strictly  absent.  Effects 
of  j)iieumatolysis  are  likewise  absent  except  in  a  few  places  along  the 
contacts  Avith  the  (puii'tz  mouzonite  where  locally  the  eft'ects  of  contact 
metamorphism  are  superimposed  on  the  older  schistosity.  The  meta- 
morphism of  the  Rand  .schist  can  in  no  sen.se  be  attributed  to  the  batho- 
lithic  invasion  of  (piai'tz  monzonite,  for  angular  fragments  of  schist  of 
various  sizes  are  commonly  to  be  found  as  inclusions  in  tlie  ([uartz 
monzonite.  with  their  schistosity  oriented  at   I'andom. 

The  oidy  process  of  recrystallization  which  will  account  for  the 
observed  facts  is  that  of  static  metamorphism  whereby  the  original 
I'ocks  wei'e  deei^ly  buried  beneath  a  tremendous  load  of  other  sediments, 
the  resulting  intense  vertical  forces,  aided  by  increased  temperatures  in 
depth  and  by  solutions  trapped  in  the  sediments,  resulting  in  the 
metamorphism. 

This  ]n'oeess  of  metamorphism  would  make  necessary  not  only  an 
unconformity  between  the  Johannesburg  gneiss  and  the  Rand  schist, 
but  an  hitervening  period  of  metamorphism  as  well,  for  the  gneisses 
appear  to  have  suffered  from  lateral  stresses,  the  schists  solely  fi-om 
vetrical  ones.  During  the  earlier  ]')eriod,  the  metamorphism  of  the 
gneisses  was  largely  completed,  wiiile  during  the  secontl  period  of 
metamorphism  the  recrystallization  of  the  Rand  schist  occurred,  the 
underlying  gneisses  being  further  effected  at  the  same  time. 

Age  of  the  Johannesburg  Gneiss  and  the  Rand  Schist. 

The  age  of  these  two  groups  of  rocks  is  believed  to  be  Archean.  The 
age  can  be  inferred  solely  from  a  consideration  of  their  petrology,  and 
comparison  with  formations  of  nearby  regions. 

In  the  El  Paso  Mountains  across  the  valley  to  the  north,  marine 
sediments  believed  to  be  Paleozoic  in  age,  though  intruded  by  quartz 
monzonite,  show  practically  no  effects  of  metamorphism.  Still  further 
north,  in  the  Inyo  Mountains,  marine  sediments  ranging  in  age  back 
to  the  Pre-Cambrian  are  similarly  l)ut  little  altered.^ 

In  the  desert  ranges  to  the  north  and  northeast,  namely  the  Argus, 
Slate,  Panamint  and  Funeral  ranges,  sedimentary  strata  ranging  from 
Cambrian  to  Permian  in  age  are  practically  nnmetamorphosed.- 

In  the  region  to  the  south,  rocks  believed  to  be  of  Paleozoic  age,  while 
more  or  less  effected  by  batholithic  invasion,  have  not  been  subjected 

'A.  Knopf  and  E.  Kirk.  A  Geologic  Reconnaissance  of  the  Inyo  Range  and  tlie 
Ea.'^tern   Slope  of  the  Sierra  Nevada,  California.     U.   S.  G.   S.  Prof.  Paper  110. 

-S.  H.  Ball.  A  Geologic  Reconnaissance  of  Southwestern  Nevada  and  Eastern 
California.     U.  S.  G.  S.  Bull.  308.      (1907.) 

J.  E.  Spurr.  Descriptive  Geology  of  Nevada  South  of  the  Fortieth  Parallel  and 
Adjacent  Portions   of   California.      U.    S.   G.    S.   Bull.   208.    (1903.) 


—  30  — 

to  the  same  intensity  of  action  suffered  by  the  rocks  of  the  Rand  Moun- 
tains.^    Further  east,  in  the  Bristol  Range,  sediments  of  Lower  and 

PLATE  9. 


« 


A.   OUTCROP  OF  RAND  SCHIST  NORTHWEST  OP  RANDSBURG.     The  schls- 
tosity    is    flat-lying    ami    conforms    to    the    bedding. 


B.   SOUTHERN   FRONT   OF   THE   EL   PASO   MOUNTAINS.      The   Garlock    Fault 
lies   behind  the  low   ridge   in   the  middle   distance. 

Middle  Cambrian,  and  Carboniferous  age  are  known  which  are  but 
little  altered. =  Still  further  east,  in  the  Grand  Canyon  section,  sedi- 
mentary strata  of  Algoukiau  age- are  not  metamorphosed.^ 

'R.  W.  Pack,  Reconnaissance  of  the  Barstow-Kramer  Region.  U.  S.  G.  S.  Bull. 
514.  pp.   141-154.    (1914.) 

-C.  W.  Clark,  Lower  and  Middle  Cambrian  Formations  of  the  Mojave  Desert. 
Bull.   Dept.   of  Geol.    Univ.   of   Calif.      Vol.    13    (1921),    pp.    1-7. 

^L.  F.  Noble.  The  Shinumo  Quadrangle,  Grand  Canvon  District,  Arizona. 
U.  S.  G.   S.  Bull.  549.    (1914.) 


I 


—  31  — 

Since  nowhere  within  this  province  or  in  adjacent  regions  have  rocks 
known  to  be  yonnger  than  the  Archean  in  age  suffered  the  same  inten- 
sity of  metamorphism  as  have  the  Johannesburg  gneiss  and  the  Rand 
schist,  these  groups  must,  at  least  until  further  evidence  is  forthcoming, 
be  considered  to  he  Archean  in  age. 

UNDIFFERENTIATED  STRATA  OF  PALEOZOIC  AGE. 

A  series  of  marine  sediments  believed  to  be  Paleozoic  in  age  outcrop 
over  a  large  portioii  of  the  El  Paso  Mountains  in  the  northwestern 
corner  of  the  quadrangle.  The  rocks  of  this  series  pass  beneath  later 
sediments  and  alluvium  to  the  northwest  and  are  cut  off  by  later  intru- 
sive quartz  monzonite  on  the  northeast.  On  the  south  they  abutt 
against  a  major  fault  line,  tlie  Garloek  Fault.  South  of  this  fault,  due 
to  a  heavy  cover  of  alluvium,  no  exposures  occur  except  near  the  fault 
in  the  central  portion  of  the  quadrangle  where  a  number  of  small  out- 
crops project  up  thi'ough  the  alluvium. 

Lithology  and  Structure. 

Tlie  rocks  composing  this  series  include  marine  limestones,  cherts, 
clay  shales,  sandstones  and  conglomerates  in  a  bedded  series  of  strata. 
Limestones  are  the  dominant  rock  type  represented,  being  closely 
folloAved  in  quantity  by  shales. 

In  consequence  of  the  limited  time  available  for  field  work  and  due 
also  to  the  absence  of  fossilif erous  horizons,  it  was  not  found  practicable 
to  subdivide  this  series  into  definite  formations.  Although  no  exact 
statement  can  be  made,  it  seems  probable  that  at  least  three  and  possi- 
bly more  distinct  groups  of  rocks  are  present. 

The  structure  of  the  beds  exposed  in  the  El  Paso  Mountains  to  the 
north  of  the  Garloek  Fault  is  broadly  simple,  although  in  detail  it  may 
be  highly  complex.  The  major  feature  is  a  steeply-folded  syneline 
whose  axis  roughly  parallels  the  trend  of  the  range  from  southwest  to 
northeast.  The  axis  plunges  at  a  steep  angle  to  the  northeast.  Only 
part  of  a  fold  is  represented,  the  northeastern  portion  having  been 
destroyed  bj'  the  batholithic  invasion  of  quartz  monzonite.  Ile'nce  a 
section  along  the  crest  of  the  range  from  southwest  to  northeast  shows  a 
simple  series  of  strata  having  a  common  dip  to  the  northeast,  the  dips 
varying  from  about  forty  degrees  near  the  western  ])order  of  the  map 
to  vertical  near  the  (juartz  monzonite  contact.  The  beds  outcropping 
along  the  front  of  the  range  north  and  northwest  from  Rand  Station, 
dip  to  the  north  and  northwest  at  angles  of  from  ten  to  thirty  degrees. 

In  detail  however,  the  structure  appears  much  more  complicated  due 
to  minor  flexures  on  the  flanks  of  the  major  fold.  Within  the  range 
faulting  appears  to  be  decidedly  subordinate  to  folding. 

South  of  the  fault  the  beds  dip  at  angles  of  twelve  to  fifteen  degrees 
to  the  north  and  northwest,  an  attitude  similar  to  the  attitude  of  the 
beds  on  the  front  of  the  range  just  north  of  the  fault. 

The  lowest  bed  exposed  in  the  quadrangle  is  a  conglomerate  which 
outcrops  on  the  south  front  of  the  El  Paso  Range  practically  at  the 
west  border  of  the  map.  Its  thickness  is  unknown.  The  bed  has  been 
tightly  squeezed  and  shows  slight  effects  of  recrystallization.  No  bed- 
ding is  apparent.  The  component  pebbles  are  chiefly  angular  and  con- 
sist predominantly  if  not  entirely  of  schist.     They  vary  from  a  half  to 


—  32  — 

about  one  and  a  half  inches  in  diameter  and  are  set  in  a  matrix  which 
appears  to  consist  of  sand  and  small  schist  flakes.  The  majority  of  the 
schist  fragments  are  dark  green  in  color  and  appear  to  be  fine-grained 
amphibole  schists.  But  the  rock  is  so  altered  that  these  fragments  can 
not  be  correlated  with  any  degree  of  certainty  with  the  schists  of  the 
Rand  Mountains. 

Approximately  the  lower  fourth  of  the  series  exclusive  of  the  con- 
glomerate at  the  base,  consists  of  claj''  shale  with  interbedded  cherts, 
limestones  and  sandstones.  The  shale  is  light  gray  in  color  and  thinly 
fissile  so  that  it  breaks  out  and  covers  the  surface  of  the  ground  with 
small  thin  flakes.  These  flakes  show  a  silvery  sheen  on  the  surface 
apparently  due  to  a  development  of  sericite.  These  shales  are  quite 
soft.  The  sandstones  are  most  pronounced  well  down  in  the  section,  a 
massive  bed  immediately  overlying  the  conglomerate.  These  sand- 
stones are  for  the  most  part  thiek-l)edded  and  highly  quartzose.  The 
cherts  and  limestones  usually  occur  in  beds  from  twenty  to  fifty  feet 
in  thickness  interstratified  with  the  shales  and  sandstones.  The  lime- 
stones are  characteristically  in  thin  bands,  one  to  two  inches  thick,  Avith 
alternate  layers  of  black  chert  less  than  a  half-inch  in  thickness.  The 
limestones  which  are  light  gray  in  color,  weather  chiefly  by  solution  so 
that  thin  layers  of  the  black  chert  are  left  as  prominent  ridges  on  the 
weathered  surface.  Both  the  limestone  and  the  chert  bands  are  cut  by 
numerous  irregular  veinlets  of  white  caleite.  The  cherts  are  black  when 
fresh,  weathering  to  a  brownish-black.  In  addition  to  occurring  inter- 
banded  with  the  limestones,  the  cherts  occur  as  thick  beds  interstratified 
with  limestone,  sandstone  or  shale. 

The  central  portion  of  the  series  shows  a  strong  development  of  hard 
siliceous  shales.  These  shales  are  strongly  banded,  the  alternate  bands 
being  black  and  either  white  or  cream  colored.  The  individual  bands 
are  usually  fairly  thin,  grading  downward  to  the  thickness  of  a  sheet 
of  paper.  On  the  weathered  surface  the  light  colored  bands  are  fre- 
quently colored  pinkish,  reddish  or  yellowish.  These  silicious  shales 
occur  interbedded  with  beds  composed  of  alternating  bands  of  gray 
limestone  and  black  chert,  or  with  beds  of  pure  quartz  sandstone.  The 
limestone-chert  beds  are  probably  the  most  characteristic  phase  of  this 
portion  of  the  series. 

The  upper  quarter  of  the  series  is  composed  chiefly  of  cream-colored 
silicious  limestones.  These  limestones  are  quite  hard  and  under  the 
microscope,  show  some  development  of  pyroxenes  and  plagioclases. 
This  partial  recrystallization  is  probably  referable  to  the  intrusion  of 
quartz  monzonite.  The  limestones  are  usually  thick  bedded  and  mas- 
sive although  locally  alternations  occur  with  thin  liands  of  black  chert. 

The  beds  exposed  south  of  the  Garlock  Fault  are  composed  chiefly 
of  black  chert,  either  with  or  without  alternating  bands  of  gray  lime- 
stone. These  beds  most  strongly  resemble  beds  of  the  central  portion 
of  the  series  to  the  north  of  the  fault. 

The  total  thickness  of  strata  represented  in  the  series  is  believed  to  be 
between  15,000  and  16,000  feet.  While  these  figures  make  no  allowance 
for  repetition  of  strata  by  faulting,  it  is  not  ])elieved  that  any  important 
repetition  has  occurred,  no  prominent  faults  having  been  observed 
within  the  area  occupied  by  this  series. 


—  33  — 

Mode  of  Accumulation. 

Such  a  thick  and  well-graded  series  of  sediments  as  those  here  repre- 
sented could  hardly  have  accumulated  under  any  but  marine  conditions. 
Excludin<ji:  the  conglomerate  at  the  base  of  the  series,  all  the  strata  give 
evidence  of  having  been  exceptionally  "well  sorted.  The  great  prepon- 
derance of  fine-grained  sediments  and  chemical  precipitates,  i.  e.  the 
shales,  cherts  and  limestones,  as  we'll  as  the  exceptional  degree  of  sort- 
ing and  rounding  exhibited  by  the  sandstones,  would  lead  to  the  belief 
that  the  accumulation  occurred  chiefly  in  rather  deep  waters  at  a 
moderate  distance  from  any  land  mass. 

Age. 

The  only  fossils  found  within  the  quadrangle  so  far  as  the  writer  is 
aware  have  come  from  this  series.  F.  L.  Hess  reports  the  finding  of  two 
forms.^     He  says  in  part: 

*  *  *  They  were  very  indistinct,  and  the  better  one  George  H.  Girty  believes 
to  be  possibly  a  Paleozoic  coral  or  sponge  and  probably  not  younger  than  Car- 
boniferous.    ♦     •     » 

The  relation  between  this  series  and  the  Rand  schist  is  not  known 
since  the  two  groups  do  not  occur  in  contact  within  the  quadrangle. 
The  great  difference  in  the  degree  of  metamorphism  which  the  two 
groups  show,  as  well  as  the'  presence  of  schist  fragments  (which  resem- 
ble types  present  in  the  Rand  schist)  in  the  conglomerate  observed  in 
the  lower  portion  of  this  series,  would  imply  that  an  unconformable 
relation  probably  exists. 

The  batholith  which  intrudes  the  series  is  believed  to  be  the  equiva- 
lent of  the  Sierra  Nevada  granodiorite,  *.  e.  late  Jurassic.  Strong 
resemblances  exist  between  this  series  and  rocks  known  to  be  of  Paleo- 
zoic age  which  occur  in  regions  to  the  north  and  east,  wliereas  known 
Mesozoic  deposits  in  the  Inyo  Mountains  to  the  north  consist  largely 
of  pyroclastic  material. - 

Considering  these  lines  of  evidence,  it  is  believed  that  the  strata  here' 
represented  are  Paleozoic  in  age,  probably  several  geologic  periods 
being  repesented. 

ATOLIA  QUARTZ  MONZONITE. 

Three  separate  areas  of  granitic  rocks  are  exposed  within  the  con- 
fines of  the  Randsburg  quadrangle.  The  largest  of  these  areas  covers 
approximately  the  lower  quarter  of  the  quadrangle.  The  second  area 
in  point  of  size,  occurs  in  the  northern  portion  of  the  quadrangle,  while 
the  third  area  is  a  small  stock-like  mass  lying  just  south  of  Randsburg. 
This  last  area  averages  slightly  over  a  half-mile  in  width  by  four  miles 
in  length,  being  irregular  in  outline. 

These  three  areas  represent  parts  of  the  same  batholithic  mass.  They 
possess  about  the  same  average  composition,  namely  that  of  a  quartz 
monzonite,  and  show  the  same  peculiarities. 

The  southern  mass  of  quartz  monzonite  is  structureless  and  quite 
uniform  in  composition  except  locally  near  the  contact  with  the  Rand 
schist  where  some  variation  is  found. 

'F.  L..  Hess.  Gold  Mining  in  the  Randsburg  Quadrangle.  Bull.  U.  S  G  S  430 
(1910),    pp.    23-47. 

=A.  Knopf  and  E.  Kirk,  U.  S.  G.  S.  Prof.  Paper  110. 
3— 37S41 


—  34  — 

The  rock  exposed  on  the  dump  of  the  Union  Mine  of  the'  Atolia  Min- 
ing Company  is  quite  characteristic  of  the  quartz  monzonite  of  this 
area.  As  seen"  in  the  hand  specimen,  this  rock  shows  a  medium-grained 
granitic  texture  and  is  composed  of  white  and  black  minerals  in  the 
ratio  of  about  five  to  one.  The  white  minerals  consist  of  orthoclase, 
plagioelase  and  quartz  in  approximately  equal  proportions.  Occasion- 
ally a  large'  orthoclase  crystal  is  to  be  seen,  up  to  an  inch  in  diameter, 
which  contains  as  poikilitic  inclusions  other  of  the  rock-forming 
minerals  of  normal  size.  The  black  constituents  consist  of  hornblende 
and  dark-colored  biotite  in  about  equal  amounts.  In  addition,  there 
occur  very  abundant  honey-yellow  crystals  of  titanite  which  vary  in 
size  from  microscopic  to  over  an  eighth  of  an  inch  across. 

The  above  described  composition  is  closely  checked  by  a  microscopical  examina- 
tion of  the  rock.  The  plagioelase  is  found  to  have  the  composition  of  andesine- 
oligoclase.  The  hornblende  is  of  the  green  variety,  while  the  biotite  is  strongly 
pleochroic  in  shades  of  yellowish-brown.  In  addition  to  the  abundant  well-formed 
crystals  of  titanite,  magnetite  and  apatite  are  present  in  moderate  amount,  and 
rarely  crystals  of  zircon  are  to  be  observed.  Some  strain  effects  are  present, 
noticeable  chiefly   in  the   distortion   of   the  biotite  flakes. 

These  features,  excepting  possibly  the  porphj^ritic  tendency  of  the 
orthoclase  which  is  probably  local,  are  believed  to  be  characteristic  of 
the  quartz  monzonite's  in  this  southern  area,  although  the  relative  pro- 
portion of  the  dark  characterizing  accessories  may  vary  somewhat  from 
place  to  place. 

The  granitic  rocks  of  the  northern  portion  of  the  quadrangle  are  not 
so  uniform  either  in  appearance  or  composition.  Although  most  com- 
monly the  rocks  have  a  composition  and  texture  quite  similar  to  those 
of  the  quartz  monzonites  of  the  southern  area,  locally  the  intrusion  has 
been  complex,  small  masses  of  varying  composition  having  been  intro- 
duced. These  smaller  and  probably  later  masses  which  seem  to  grade 
into  the  main  rock  mass  are  in  general,  slightly  more  basic  than  the 
main  quartz  monzonite  intrusive,  usuallj^  having  the  composition  of  a 
quartz  diorite  or  of  a  grandiorite.  The  characterizing  accessory 
minerals  may  be  more  abundant  than  in  the  main  quartz  monzonite  or 
in  other  cases  they  may  be  entirely  absent. 

At  a  number  of  places  in  the  northern  part  of  the  Lava  Mountains 
there  occur  granitic  rocks  which  are  noticeably  red  in  color  and  which 
vary  in  composition  from  quartz  diorites  to  quartz  monzonites.  As  seen 
in  the  hand  specimen,  the  rock  possesses  a  medium  fine  and  somewhat 
uneven-grained  granitic  texture.  Accessory  minerals  are  practically 
absent,  the  constitutent  minerals  being  milky  quartz  and  light  red 
feldspar.     The  feldspar  shows  no  twinning  striations. 

Microscopically  the  feldspars  are  found  to  be  largely  acid  oligoclase  with  only  small 
amounts  of  microcline.  The  quartz  in  different  specimens  varies  from  ten  to  fifty  per 
cent.  Green  hornblende  and  muscovite  may  be  present  in  traces.  The  minor 
accessories  arc  absent  or  nearly  so.  The  most  interesting  feature  of  this  rock  Is 
•the  strain  effects  present.  The  quartzes  show  undulatory  extinction,  while  occasion- 
ally the  albite  twinning  lamellae  of  the  feldspars  show  a  pronounced  curvature 
Much  of  the  rock  is  brecciated,  the  fragments  being  cemented  by  a  later  generation 
of  fine-grained  quartz.  The  cementation  produced  no  alteration  of  the  feldspars. 
Seemingly  the  brecciation  and  recementation  must  have  followed  closely  on  the 
original  intrusion. 

Much  of  the  material  derived  from  the  railroad  tunnel  north  of 
Summit   Diggings  consists  of  medium-coarse   but  somewhat   uneven- 


PLA'I  K  in. 


A.    QUARTZ     MONZONITE.        A  =  andesine;     Q  =  quartz  ;     H  =r  horn- 
blonde ;    B  =  biotite;    P^raugite.       50    dia.       X    nicols. 


B.  QUARTZ  AIOXZONITE.  A=:andesine;  O  =  orthoclase  ;  B  =  biotite; 
H  -r  hornblende  ;  T  ==  titanlte  ;  M  =  magnetite.  Note  how  the  ortho- 
clase  forms  a  'groundmass'  for  the  other  minerals.  50  dia.  X  nicols. 


37841— facing  p.   34. 


—  35  — 

grained  granitic  rocks  wliose  composition  varies  from  quartz  diorite 
to  quartz  monzonitc.  Some  of  these'  rocks  are  rather  dark  colored  due 
to  the  abundant  ferromagiiesian  minerals  present.  In  the  hand  speci- 
men, feldspars,  (puirtz,  biotite  and  hornblende  can  be  recognized.  The 
majority  of  the  feldspars  are  faintly  pink  in  color,  only  a  few  showing 
albite  twinning  striations. 

Microscopically  the  feldspar  is  found  to  he  larffoly  an  acid  andesine  with  varyinj? 
but  usually  subordinate  amounts  of  orthoclase  and  luicrocline.  Quartz  while  abun- 
dant is  usually  present  in  loss  quantity  than  the  feldspars.  The  hornblende  is  of 
the  green  to  light-brown  variety,  and  is  about  equaled  in  quantity  by  brown  biotite. 
.Magnetite  is  usually  abundant  in  small  rounded  grains.  Moderate  amounis  of  augite 
occur  either  as  cores  in  the  centers  of  crystals  of  hornblende  or  as  narrow  reaction 
rims  surrounding  the  grains  of  magnetite.  Traces  of  apatite  and  zircon  complete 
the  mineral  composition.  Intense  strain  effects  are  common,  usually  shown  by 
undulatory  extinction  of  the  quartzes,  by  bent  biotite  lamella^,  or  in  a  few  cases 
ob.served  by  actual  bending  of  the  albite  twinning  lamellae  of  the  plagioclases. 

In  the  vicinity  of  the  El  Paso  Peaks  variations  in  the  composition  and 
textures  of  the  plutonic  rocks  are  quite  noticeable.  The  composition 
seldom  departs  far  from  that  of  a  quartz  monzonitc  howeve'r. 

The  small  stock-like  mass  south  of  Kandsburg  is  the  most  variable 
of  the  three  areas  of  plutonic  rocks.  This  area  is  in  reality  a  complex, 
containing  included  fragments  of  foreign  rocks  which  range  in  size  up 
to  several  hundred  feet  in  diameter.  Most  of  these  fragments  are  from 
the  adjoining  Rand  schist,  but  as  has  been  pointed  out  earlier  in  this 
paper,  two  large  xenoliths  of  the  Johannesburg  gneiss  occur.  Within 
the  area  as  mapped,  there  exists  a  series  of  granitic  types  of  rocks 
which  includes  diorites,  quartz  diorites,  granodiorites,  quartz  monzo- 
nites,  monzonites  and  granites.  Aplites  are  also  represented.  As  in  the 
two  larger  areas  the  major  type  represented  is  a  quartz  monzonitc. 
The  textures  vary  also  but  not  so  widely  as  does  the  composition.  Over 
most  of  the  area  the  rocks  are  from  medium  to  coarse-grained  granitic, 
but  locally,  especially  near  the  borders  of  the  intrusive  they  pass  into 
finer-grained  types.  In  places  large  phenocrysts  of  orthoclase  up  to  an 
inch  in  diameter  stand  out  on  the  weathered  surface  of  the  rock. 

An  especially  interesting  type  represented  is  an  orbicular  quartz 
diorite  which  is  present  in  several  parts  of  the  area  but  is  especially 
well  developed  to  the  east  of  the  highway  just  southeast  of  Randsburg. 
In  the  field  this  rock  apj)ears  as  a  coarse-grained  and  apparently  normal 
granitic  rock,  through  which  are  scattered  more  or  less  rounded  dark 
masses  of  a  fine-grained  granitic  rock  of  all  sizes,  from  a  foot  or  more 
in  diameter  down  to  an  inch.  The  orbicles^  range  from  spheroidal 
to  flat  and  angular  in  form. 

Occasionally  several  of  these  orbicles  are  strung  out  in  a  row,  with 
the  adjacent  boundaries  possessing  a  common  form  so  that  if  the  inter- 
vening granitic  matrix  were  removed  the  several  orbicles  could  be  fit 
together  to  form  a  shigle  larger  mass.  (See  Figure  2.)  The  boundaries 
between  the  orbicles  and  the  granitic  matrix  while  quite  definite  are 
gradational. 

'The  term  'orbicle'  is  used  here  to  denote  a  rounded,  subangular  or  angular 
mass  which  is  imbedded  in  a  granitic  matrix  and  which  is  characterized  by  a 
granitic  texture,  sometimes  porphyritic,  and  an  excessive  development  of  ferromag- 
nesian  minerals.     Radial  or  concentric  structures  may  or  may  not  be  developed. 


—  se- 
ll! the  hand  specimen  the  granitic  matrix  is  found  to  possess  an 
ordinary  medium  coarse-grained  granitic  texture  and  is  composed  of 
light-colored  and  dark-colored  constituents  in  the  ratio  of  about  five  to 
one.  The  light-colored  constituents  were  observed  to  be  chiefly  white 
feldspar  crystals  and  moderate  amounts  of  quartz.  Most  of  the  feld- 
spars show  albite  twinning  striations.  The  dark  constituents  consist 
chiefly  of  flakes  of  brown  mica  and  subordinate  amounts  of  hornblende. 

Microscopically,  in  the  sections  examined,  the  rock  was  found  to  vary  from  a 
quartz  diorite  to  a  granodiorite.  The  most  abundant  feldspar  was  a  basic  oVigo- 
clase.  Orthoclase  was  subordinate.  Quartz  was  moderately  abundant.  The 
accessory  minerals  were  chiefly  brown  biotite  with  minor  amounts  of  green  horn- 
blende and  augite.     Small  amounts  of  magnetite,  apatite  and  zircon  were  present. 


The  orbieles  also  show  a 
granitic  texture  but  are  quite 
fine  grained.  The  light  and 
dark-colored  minerals  are  pres- 
ent in  the  ratio  of  about  two 
to  one,  the  light  minerals  con- 
sisting predominantly  of  feld- 
spar ;  the  dark  minerals  being 
largely  biotite.  Scattered 
through  this  granitic  ground- 
phenocrysts    in    well-formed    equant 


Figure  2.  Orbieles  whose  appearance  sug- 
gests that  they  once  formed  a  single  mass. 
About   1/10  natural  size. 


mass   are   occasional   plagioelast 
crystals  up  to  an  eighth  of  an  inch  across 


The  feldspar  was  found  under  the  microscope  to  consist  entirely  of  plagioclase 
having  the  composition  of  andesine  ( Ab,.,„Anj„ ) .  The  biotite  is  of  the  brown  variety. 
.Small  and  usually  rounded  crystals  of  augite  occur  to  about  five  per  cent  of  the 
total  composition  of  the  rock.  Abundant  small  needles  of  apatite  and  occasional 
irregular  patches  of  magnetite  are  found  as  inclusions  in  the  plagioclases.  While 
hornblende  was  absent  from  some  sections,  in  others  it  appeared  in  important 
amount.  Likewise  quartz,  though  usually  absent,  was  in  one  case  present  in  fair 
(juantity. 

Microscopically   these  orbieles  api>ear  to  jwssess  a  normal  granitic  texture. 


At  numei'ous  places  in  this  area  intrusive  contact  zones  occur  between 
the  Atolia  (piartz  monzonite  and  the  Rand  schist,  in  Avhich  abundant 
flat  angular  fragments  of  the  schist  are  scattered  through  the  granitic 
rock.  Such  zones  with  their  included  fragments  are  believed  to  be 
the  forebears  of  the  orbicular  rocks  of  the  region,  the  orbieles  being 
only  later  stages  of  the  inclusions  whose  shapes  have  been  modified  by 
resorbtion  and  whose  composition  has  been  modified  by  diffusion.  The 
last  stage  of  the  process  would  be  the  complete  assimilation  of  the 
orbieles  and  their  total  disappearance  in  the  granitic  matrix. 

In  the  field  the  writer  observed  all  gradations  from  included  angular 
fragments  of  schists  possessing  their  original  composition  and  texture, 
through  angular  fragments  showing  only  a  trace  of  a  schistose  texture 
and  apparently  modified  in  composition,  to  rounded  orbieles  with 
granitic  texture  and  the  composition  of  a  quartz  diorite  and  finally  to 
places  where  only  the  faintest  concentration  of  dark  minerals  remained 
to  suggest  the  former  presence  of  an  orbicle. 

One  highly  angular  fragment  found  isolated  in  the  quartz  monzonite  only  a  short 
distance  from  the  contact  west  of  the  highway  just  southeast  of  Randsburg  showed 
sharp   edges   and   appeared   to   be   bounded   in   part  by   what   had   been   a   schistose 


PLATE   11. 


A.    THIN     SECTION     OE     ORBICLE.        P  =  plagioclase ;     B  =  biotite ; 
H  =  hornblende.      30  dia.      Ordinary  light. 


B.   QUARTZ-EPIDOTE   ROCK.      From   veinlet   in   Quartz   monzonite. 
Br— epidote;  Q  =  quartz.      50  dia.     Ordinary  light. 


37841 — facing  p.  36. 


Ii 


—  37  — 

cleavage.  Traces  of  the  former  schistosity  could  ho  made  out  iu  the  mass  of  the 
rock.  Under  the  microscope  the  composition  and  texture  were  found  to  be  quite 
similar  to  those  of  the  rounded  orbicles,  differing  only  in  the  feldspar  being  oligo- 
clase  instead  of  andesine,  in  the  presence;  of  alnmdant  green  hornblende  and  tlie 
absence  of  augite.     The  texture  was  fine-grained,  granitic. 

Relation  to  Adjacent  Formations. 

The  Atolia  quartz  iiionzonite  is  intrusive  into  tlie  Rand  schist  and 
the  nnditferentiated  l^deozoie  series  of  the  El  Paso  \M()nntains.  This 
batholithic  invasion  liad  no  ctTecl  in  cnntrollin^-  or  modifyino-  the  types 
of  rocks  found  in  the  fJohannesl)urg'  gneiss  or  tlie  Rand  schist  groups, 
except  near  the  contact,  and  its  Jieneral  effects  in  modifying  the  Paleo- 
zoic series  appear  to  have  been  very  slight. 

The  contact  between  the  Rand  schist  and  the  southern  area  of  quartz 
monzonite  is  believed  to  be  in  ])art  a  fault  contact.  Locally,  however, 
this  contact  is  certainly  one  of  intrusion.  One-half  mile  west  of  the 
Rand  C'ontact  Mine,  near  the  ])ower  line,  the  limestone  adjacent  to  the 
contact  shows  a  development  of  a  deep-green  mineral,  apparently 
epidote.  Still  further  west  on  this  contact,  in  the  southwestern  portion 
of  the  Hand  ^lountains,  the  (piartz  monzonite  cuts  across  to  the  north 
side  of  the  mountains.  The  mai)ping  in  this  portion  of  the  area  clearly 
brings  out  the  intrusive  nature  of  the  (jnartz  monzonite,  while  at  a 
number  of  places  contact  minerals  are  found  develo])ed  in  the  adjoining 
rocks.  The  schists  are  not  much  affected  adjacent  to  the  intrusive, 
hardening  and  the  loss  of  the  schistose  cleavage  being  the  chief  altera- 
tions observed.  The  limestones,  however,  commoiily  show  a  megascopic 
development  of  large  crystals  of  dark-colored  hornblende  and  reddish- 
brown  garnet. 

In  the  region  of  the  El  Paso  Peaks,  in  the  northern  part  of  the  quad- 
rangle, strong  contact  zones  are  developed.  The  El  Paso  Peaks  them- 
selves are  capped  with  a  heavy  dark  greenish-lilack  rock  which  is 
composed  chiefly  of  dark-green  epidote  and  brown  garnet,  witli  lesser 
(piantities  of  coarsely  crystalline  calcite,  quartz  and  lead-gray  metallic 
plates  of  specular  hematite  which  at  times  ai)pear  ruby-red  by  trans- 
mitted light.  This  I'ock  is  coarsely  crystalline  and  quite  massive. 
Occasional  masses  consisting  almost  entirely  of  epidote  are  found,  the 
epidote  occurring  either  as  porous  aggregates  of  ititerlocking  crystals 
or  as  large  compact  radiating  crystalline  masses  several  inches  in 
length. 

Further  south,  coarsely  crystalline  rocks,  composed  of  augite,  horn- 
blende, calcite,  pyrite  and  more  or  less  epidote,  were  observed.  Locally, 
garnet  was  developed.  The  workings  of  the  Hummer  Mine  are  princi- 
pally in  rocks  of  this  character. 

Along  most  of  this  contact,  however,  the  Paleozoic  limestones  offer 
little  or  no  visual  evidence  that  they  have  suffered  from  an  igneous 
intrusion. 

Contact  zones  are  well  developed  a  half-mile  southeast  of  Randsburg, 
both  along  the  contact  and  in  the'  enclosed  xenoliths  (possibly  Johannes- 
burg gneiss  xenoliths  in  part)  within  the  quartz  monzonite.  Here  the 
limestones  have  been  altered  to  rocks  composed  of  dark  reddish-brown 
garnets  and  dark  green  diopside.  These  rocks  are  usually  massive,  but 
in  a  few  exposures  are  coarsely  banded,  the  banding  resulting  from 
the   development   of   alternate   layers   of   green   diopside   and   brown 


—  38  — 

srariiet.  Microscopically  abundant  plagioclase  (labradorite)  and  some 
calcitef  are  fonnd  to  occui-  intergroAvn  Avith  the  ^rarnet  and  diopside. 
T^nlike  the  other  contact  rocks  observed,  the  garnets  of  these  banded 
varieties  are  well  formed  crystals  about  an  eighth  of  an  inch  in 
diameter.  These  rocks  weather  chiefly  by  solution  of  all  the  minerals 
except  the  garnets,  so  that  on  a  weathered  surface  the  garnets  stand  out 
as  small  spheroidal  bodies,  many  of  which  show  crystal  faces. 

After  Effects  of  the  Batholithic  Invasion. 

Aplite  and  pegmatite  dikes  are  occasionally  met  with,  but  nowhere 
within  the  confines  of  the  quadrangle  do  they  show  a  strong  develop- 
ment. Just  outside  of  the  confines  of  the  quadrangle,  in  the  prominent 
hill  north  of  the  Kandsburg-Mojave  road,  pegmatite  dikes  become 
locally  abundant.  They  are  characteristically  developed  as  coarsely 
crystalline  graphic  intergrowths  of  cream  to  flesh-colored  orthoclase 
and  quartz,  with  sporadic  flakes  of  dark-colored  mica.  Scattered 
through  the  rock  and  quite  commonly  imbedded  in  the  orthoclase 
crystals  are  abundant  minute  crystals  of  wine-colored  garnet.  Most 
of  the  dikes  observed  were  less  than  three  feet  in  width. 

Epidote  is  strongly  developed  as  a  late  magmatic  mineral  in  all 
portions  of  the  quartz  monzonite  terraine,  possibly  excepting  the  small 
stock-like  mass  to  the  south  of  Randsburg.  It  is  most  characteristically 
developed  as  a  fine-grained  intergrowth  with  quartz,  occurring  in  small 
dikes  or  veins  cutting  the  quartz  monzonite'.  These  dikes  or  veins  vary 
in  thickness  from  about  two  inches  down  to  a  small  fraction  of  an  inch. 
In  many  parts  of  the  area  heavy,  finely  crystalline,  light  gi'cen-colored 
fragments  derived  from  these  veins  or  dikes  can  be  picked  up  on  the 
surface.  Epidote  was  also  observed  in  some  of  the  granitic  rocks,  both 
from  the  northern  and  southern  portions  of  the  quadrangle,  associated 
with  horiiblende  and  biotite  and  apparently  a  primary  mineral.  The 
occurrence  of  epidote  in  the  El  Paso  Peaks  contact  zone  has  already 
been  described. 

Large  bunches  of  white  'bull'  quartz  up  to  fifty  feet  or  more  in 
diameter  are  commonly  met  Avith  in  the  field,  either  cutting  the  quartz 
monzonite.  or  any  of  the  older  formations,  being  especialh'  common  in 
the  Rand  schist.  These  masses  probably  represent  faulted  segments 
of  veins  in  part.  While  usually  quite  barren  of  any  mineral  other  than 
the  massive  glassy  quartz,  locally  these  veins  carry  abundant  coarsely 
crystalline  and  commonly  radiating  light-green  epidotes,  and  more 
rarely  large  crystals  of  pink  orthoclase  and  flakes  of  either  light  or  dark 
micas.  These  veins  Avere  formed  under  conditions  of  high  temperature 
and  high  pressure,^  possibly  in  part  approaching  conditions  under 
which  the  pegmatites  form,  and  hence  are  probably  closely  related  to 
the  invasion  of  the  quartz  monzonite.  These  veins  are  described  in 
this  portion  of  the  paper  because  they  are  not  known  to  possess  any 
economic  value. 

Correlation  of  the  Three  Areas  of  Quartz  Monzonite. 

The  correlation  of  the  three  areas  of  granitic  rocks  as  being  parts  of 
the  same  batholithic  invasion  is  made  for  the  following  reasons.     (1) 

'According  to  Lindgren's  classification,  tliese  veins  would  be  termed  hypothermal. 
W.  Lindgren.  A  Suggestion  for  the  Terminology  of  Certain  Mineral  Deposits.  Econ. 
Geol.,  Vol.   17.    (1921),   pp.    292-294. 


—  39  — 

The  areas  are  similar  in  i^eneral  eomposition  though  locally  somewhat 
variable  iu  the  vicinity  of  the  intrusive  contacts.  (2)  At  least  two  of 
the  areas,  those  in  the  northern  and  southern  parts  of  the  quadrangle, 
possess  similar  peculiarities — namely,  the  strong  development  of  late 
magmatic  epidote.  Epidote  is  also  found  in  the  quartz  veins  believed 
to  be  associated  with  and  located  not  far  distant  from  the  central  area 
of  granitic  rocks.  (3)  The  granitic  rocks  are  intrusive  into  all  rocks 
in  the  quadrangle  of  Paleozoic  age  or  older.  The  southern  area  of 
quartz  monzonite  continues  to  the  southea.st  for  fifteen  miles  where  in 
the  vicinity  of  the  Silver  Dome  Mine  it  is  found  to  intrude  a  series  of 
sedimentary  strata  not  unlike  those  of  the  El  Paso  Mountains  and  pre- 
sumably of  Paleozoic  as^e.  (4)  There  is  an  entire  absence  of  any 
evidence  which  would  even  suggest  the  presence  in  this  quadrangle  of 
an  older  batholithic  invasion. 

The  three  areas  of  quartz  monzonite  as  mapped  are  believed  to  be 
actually  connected  with  each  other  beneath  the  later  cover  of  Tertiary 
sediments  and  lavas  present  in  the  eastern  portion  of  the  quadrangle. 

The  contact  between  the  Rand  schist  and  the  southern  area  of  quartz 
monzonite  was  traced  approximately  bj'  means  of  prospect  shafts  for 
a  distance  of  nearly  a  mile  beyond  the  place  where  it  passes  beneath  the 
cover  of  alluvium.  The  contact  maintains  a  course  of  about  N.  25°  E. 
The  Chicken  Hawk  shaft  and  the  Big  Six  shaft  lie  to  the  southeast  of 
the  quartz  monzonite-schist  contact,  both  having  etitered  the  quartz 
monzonite  at  moderate  depths.  The  Navajo  (Grady  No.  1)  shaft  is 
in  the  schist. 

The  last  known  point  on  the'  contact  between  the  schist  and  the 
southern  part  of  the  small  central  area  of  quartz  monzonite  is  in  the 
crosscut  from  the  Fox  Lease  shaft  where  the  contact  was  cut  at  a 
distance  of  250  feet  southeast  of  the  shaft.  Thus,  at  the  last  known 
points  the  two  contacts  are  less  than  a  mile  apart  and  are  approaching 
each  other  at  an  angle  of  about  sixty  degrees. 

Similarly  the  east  end  of  the  northern  contact  of  the  central  area  of 
quartz  monzonite  is  swinging  as  though  to  join  with  the  quartz  mon- 
zonite of  the  northern  part  of  the  Lava  Mountains,  six  miles  distant. 

Figure  3  shoAvs  the  probable  extension  of  the  quartz  monzonite 
beneath  the  cover  of  alluvium.  Tertiary  sediments  and  volcanics. 

Mechanics  of  Intrusion. 

Evidence  that  the  batholithic  invasion  occurred  both  by  assimilation 
of  the  invaded  rocks  and  by  injection  was  found  in  studying  the  Atolia 
quartz  monzonite.     The  former  process  was  the  major  one. 

The*  evidence  of  injection  is  chiefly  found  in  the  broken  and  distorted 
condition  of  portions  of  the  Rand  schist  surrounding  the  intrusive  in 
the  central  part  of  the  quadrangle.  This  portion  of  the  intrusive  repre- 
sents a  cupola  of  the  main  batholith,  and  the  injection  which  is  a  feature 
of  this  mass  is  believed  to  have  had  only  a  local  importance. 

Evidence  of  assimilation  is  more  widespread.  One  of  the  major  lines 
of  evidence,  the  orbicular  diorites,  has  already  been  described.  A 
second  line  of  evidence  is  found  in  the  observation  that  the  amount 
of  limestones  found  on  the  contacts  with  the  quartz  monzonite  is  wholly 
out  of  proportion  to  the  quantity  of  limestones  present  in  the  adjacent 
rocks.  And  wherever  a  limestone  and  some  other  type  of  rock  occur 
together  in  contact  with  the  quartz  monzonite,  the  limestone  will  usually 


—  40  — 


project  out  into  the  quartz  monzonite  far  beyond  the  other  rock.  In 
addition  it  may  be  pointed  out  that  the  inclusions  found  in  the  quartz 
monzonite  consist  of  limestone  much  more  commonly  than  would  be 
expected. 


i 


III 


Figure  3.   Shaded    area    represents    portion    of    quadrangle    in    which    the    Atolia 
quartz  monzonite  would  outcrop  if  the  Tertiary  and  later  deposits  were  removed. 

Limestones  compose  only  a  small  portion  of  the  Rand  schi.st,  certainly 
less  than  five  per  cent  of  the  whole  and  probal)ly  only  two  or  three  per 
cent.  And  yet  limestones  occur  along  from  one-fourth  to  one-third  of 
the  exposed  portion  of  the  contact  with  the  southern  area  of  quartz 
monzonite. 


i 


—  41  — 

In  the  vicinity  of  Randsbiirg  three  prominent  reentrants  of  the 
limestones  into  the'  quartz  raonzonite  are  brought  out  in  the  mapping:. 
All  three  show  on  the  geological  map,  one  on  the  south  contact  about 

PLATE  12. 


A.    ORBICUL.VR   QU.\.RTZ   DIORITE.    Exposed   three-fourths   of  a   mile   southeast 

of    Randsburg. 


■•.-^!fe»^ 


%f*'/  J^'S 


B.  WB.\THERING   IN   THE   ROSAMOND    SERIES.      Exposure   north   of    Bedrock 

Spring. 

;i  mile  fi-om  Kandsburg  and  just  west  of  the  highway.  The  second 
just  out  of  l\andsl)urg  on  the  north  contact  a  quarter  of  a  mile  east 
of  the  highway ;  the  third  on  the  same  contact  a  quarter  of  a  mile 
further  east.  * 


—  42  — 

This  superabundance  of  the  limestones  along  the  contacts  and  as 
inclusions,  and  the  tondencj^  of  the  limestones  to  project  into  the  quartz 
nionzonite  are  believed  to  be  due  to  the  limestone  being  less  susceptible 
to  assimilation  than  the  other  rock  types  present. 

Age. 

Within  the  quadrangle  the  quartz  monzonite  is  known  to  be  younger 
than  the  series  of  Paleozoic  sediments  which  may  be  Carboniferous 
in  part.  And  they  unconformably  underlie  a  series  of  sediments  which 
date  in  age  back  to  the  middle  Miocene. 

To  the  north  and  northwest,  however,  more  or  less  continuous  expos- 
ures of  plutonic  rocks  occur  which  finally  pass  into  the  quartz  mon- 
zonites  of  the  Inyo  Mountains  and  the  quartz  monzonites,  granites  and 
related  rocks  of  the  Sierra  Nevada.  The  plutonic  rocks  of  both  these 
areas  are  known  to  be  late  Jurassic  or  possibly  early  Cretaceous^  in  age. 
The  nearest  exposures  in  the  Sierra  Nevada  are  less  than  fifteen  miles 
distant  from  the  region  of  the  El  Paso  Peaks. 

There  can  be  little  doubt  but  that  the  Atolia  quartz  monzonite  is 
the  correlative  of  the  plutonic  rocks  of  the  Sierra  Nevada  and  of  the 
Inyo  Mountains  and  is  itself  probably  late  Jurassic  in  age. 

THE   ROSAMOND  SERIES. 

The  Rosamond  series,  continental  in  origin,  and  consisting  chiefly 
of  stratified  conglomerates,  feldspathic  sandstones  and  clays,  either  out- 
crops or  underlies  later  deposits  over  about  one-third  of  the  area  of  the 
quadrangle,  chiefly  in  the  east-central  portion. 

The  largest  exposures  occur  about  the  base  of  Red  Mountain  and 
in  the  north-central  portion  of  the  Lava  Mountains.  Beds  of  the  Rosa- 
mond series  presumably  underlie  the  whole  area  covered  by  the  lavas 
of  Red  Mountain  and  the  Lava  Mountains.  Passing  out  of  the  area 
mapped,  northeast  from  the  exposures  in  the  Lava  Mountains,  large 
areas  of  Rosamond  strata  are  found  which  are  not  covered  by  later 
lava  flows.  Other  prominent  occurrences  are  found  in  the  vicinity  of 
Summit  Diggings  and  in  the  region  half-way  between  Summit  Diggings 
and  Johannesburg,  with  smaller  exposures  occurring  on  the  summit  of 
the  El  Paso  IMountains  just  south  of  the  Hummer  ]Mine  and  in  the  valley 
on  the  northwest  side  of  the  El  Paso  Mountains.  This  valley  is  pre- 
sumably underlain  by  Rosamond  beds  which  continue  on  and  constitute 
the  main  mass  of  Black  ]\Iountain.  five  miles  to  the  west. 

The  area  covered  by  alluvium  south  and  southeast  of  Summit 
Diggings  is  likewise  considered  to  be  largely  underlain  by  Rosamond 
strata  of  which  occasional  small  outcrops  are  found. 

Evidence  of  former  extensions  of  the  series  is  found  in  the  occurrence 
of  two  small  blocks  of  feldspathic  sandstones  lithologically  similar  to 
sandstones  occurring  in  the  Rosamond  elsewhere  in  the  quadrangle. 
One  of  these  blocks  was  found  faulted  in  the  schist  a  mile  southeast  of 
Randsburg  just  west  of  the  forks  in  the  highway.  The  second  occur- 
rence which  was  also  a  fault  block,  was  found  near  the  tongue  of  quartz 
monzonite  in  the  west  end  of  the  Rand  Mountains.  Neither  occurrence 
was  large  enough  to  map. 

'A.  Knopf  and  E.  Kirk.     U.  S.  G.  S.  Prof.  Paper  110. 


I 

1 


—  43  — 

These  two  occurrences,  in  conjunction  with  the  small  area  on  the 
summit  of  the  El  Paso  Mountains  would  sufrprest  that  at  one  time  the 
Rosamond  series  may  have  covered  much  of  the  quadrangle. 

Lithology. 

As  has  already  been  indicated,  the  Rosamond  series  consists  largely 
of  stratified  deposits  of  conglomerates,  feldspathic  sandstones  and 
clays,  with  some  admixed  volcanic  material,  most  of  which  have  been 
but  poorly  consolidated.  Lesser  quantities  of  other  types  of  rocks 
occur. 

The  sandstones  are  by  far  the  most  abundant  as  well  as  the  most 
characteristic  beds  represented.  They  vary  greatly  in  appearance,  size 
of  material  and  composition  of  the  individual  grains,  but  possess  the 
common  feature  of  being  composed  of  poorly  Aveathered  materials. 

Practically  all  the  minerals  found  in  the  quartz  monzonite  and  schists 
of  the  region  are  represented  in  these  sandstones.  Quartz  as  might  be 
expected  is  the  most  abundant  constituent  but  may  be  approached  in 
quantity  by  the  feldspars.  The  feldspars  are  white  or  faint  pink  in 
color  and  quite  commonly  show  fresh  lustrous  cleavage  faces.  They 
are  most  conmionly  plagioclases.  Dark  colored  flakes  of  maea  are 
usually  moderately  abundant  while  occasional  grains  of  amphiboles  or 
pyroxenes  are  observed.  Many  of  the  larger  grains  are  composed  of 
rock  of  the  various  types  found  in  this  region. 

The  sands  are  usually  but  poorly  sorted,  fine  sands,  coarse  sands  and 
pebbles  usually  occurring  together  in  the  same  bed.  In  shape  the 
individual  grains  are  characteristically  subangular  to  highly  angular 
although  in  many  cases  well-rounded  grains  may  be  seen.  Over  most 
of  the  area  the  beds  are  porous  and  show  little  induration  and 
practically  no  cementation,  so  that  the  m/aterial  may  be  crumbled 
between  one's  fingers.  Locally  however  the  beds  have  been  highly 
silicified  by  hydrothermal  agencies.     (See  page  50.) 

The  sandstones  of  different  horizons  differ  greatly  in  color.  The 
most  conmion  colors  represented  include  greenish-gray,  cream,  buff  and 
deep  red  or  maroon.  These  colors  are  independent  of  weathering  on  the 
present  surface  since  mJatorial  removed  from  depths  of  several  hundred 
feet  in  shafts  in  tlie  vicinity  of  Osdiek  is  highly  colored. 

Locally  stray  pebbles  and  boulders  may  be  found  in  any  of  the 
sandstones.  By  an  increased  admixture  of  these  coarser  phases  the 
sandstones  pass  over  into  conglomeritic  sandstones  and  finally  into 
sandy  conglomerates.  In  no  case  observed  did  the  coarser  portion  of 
the  conglomerate  exceed  fifty  per  cent  of  the  whole,  the  balance  being 
sands  of  varying  degrees  of  fineness. 

The  size  of  material  present  in  these  sandy  conglomerates  varies 
greatly  from  place  to  place.  Pebbles  and  boulders  of  all  sizes  up  to 
two  feet  in  diameter  may  be  found.  Nor  does  such  coarse  material 
appear  to  be  confined  to  any  particular  horizon.  In  the  saddle  just 
west  of  the  hill  in  the  center  of  the  map  which  is  mapped  as  rhyolite,  a 
heavy  sandy  conglomerate  in  the  basal  portion  of  the  Rosamond  is 
exposed  which  is  composed  of  boulders  of  quartz  monzonite  up  to  and 
possibly  exceeding  two  feet  in  diameter.  Immediately  underlying  the 
lava  flows  on  the  south  end  of  Red  Mountain  and  at  a  horizon  apparently 


—  44  — 

well  up  in  the  Rosamond  series,  a  conglomeritic  sandstone  occurs  con- 
taining boulders  over  a  foot  in  diameter. 

In  tlie  lower  portion  of  the  series  the  ])oulders  and  pebbles  observed 
consist  solely  of  granitic  rocks  and  of  schists.  The  schists  of  these 
fragments  appear  to  be  identical  in  character  with  those  now  exposed 
in  the  Rand  ^Mountains.  In  the  upper  horizons  boulders  and  pebbles 
of  granitic  rocks  and  schist  fragments  are  equally  common  but  in 
addition  numerous  pebbles  and  boulders  of  light-colored  porphyritie 
rhyolite  and  dark-colored  diabase  appear.  AVhile  some  of  these  pebbles- 
are  moderately  well  rounded,  most  of  them  are  distinctly  angular  with 
rounded  edges.  These  detrital  rhyolite  and  diabase  fragments  appear 
to  be  identical  in  appearance,  composition  and  texture  wdth  the  rhyo- 
lites  and  diabases  known  to  be  intrusive  into  the  lo\Aier  portion  of  the 
Rosamond  series.  The  absence  of  these  fragments  in  the  lower  horizons 
of  the  Rosamond  makes  it  certain  that  they  have,  in  the  vicinity  of  Red 
Mountain,  been  derived  from  the  erosion  of  the  intrusives  in  question. 
In  addition,  at  a  number  of  places  well  up  in  the  series  subangular 
pebbles  of  a  reddish-brown  porphyritie  rock  with  a  glassy  groundmass 
were  found  which  strongly  resembled  types  found  in  the  Red  ^Mountain 
andesites. 

At  various  horizons,  beds  of  clay,  which  may  be  in  part  admixed  with 
tuffaceous  material  occur  interstratified  with  the  sandstones.  These 
beds  are  quite  subordinate  in  amount  as  compared  with  the  sandstones. 
They  vary  in  color  almost  as  widely  as  do  the  sandstones,  grayish-green, 
cream,  ])uff  and  pure  white  beintf  common  colors.  Tlie  clays  proper  are 
quite  fine  in  grain  but  usually  a  few  rounded  sand  grains  or  occasionally 
even  a  larger  fragment  may  be  present.  At  times  traces  of  stratifica- 
tion may  become  apparent  through  these  sand  grains  being  arranged 
in  layers. 

These  clays  are  usually  (|uite  soft  and  on  the  surface,  porous. 
Locally  however  as  wath  the  sandstones  they  have  been  highly  silicified 
by  hydrothermal  agencies.  In  these  cases  the  resulting  rock  is  not 
unlike  a  light  colored  acid  lava  in  appearance.  They  can  usually  be 
distinguished  however  by  the  presence  of  occasional  rounded  sand 
grains. 

The  tufFaceous  phases  are  ([uite  similar  in  general  appearance  and 
coloi-  to  the  j)ure  clays,  hut  can  he  icUMitified  ]\v  tlie  presence  of  scattered 
shai'i)-edged  angular  fragments  of  dark-colored  lavas.  The  tuffaceous 
horizons  observed  by  the  ^^^iter  were  all  well  towards  the  top  of  the 
series. 

The  clay  beds  are  quite  commonly  clmracterized  by  scattered  flakes 
and  fi-agments  of  gy psiun.  Or  the  gypsum  may  occasionally  be 
developed  in  a  thin  bed  or  seam.  Locally  round  limy  concretions  up  to 
several  inches  in  diameter  occur,  as  on  the  lower  slope  of  Red  Mountain, 
in  the  canyon  east  of  the  Big  Four  sliaft,  while  at  times  thin  seams  or 
beds  of  crystalline  ealcite  may  be  found. 

In  the  central  part  of  the  Lava  Mountains  erosion  has  cut  through 
the  base  of  the  lavas  exposing  the  underlying  Rosamond  beds  in  a  small 
moon-shaped  area.  In  this  locality  a  bed  of  gray  limestone  some  two  or 
three  feet  in  thickness  is  exposed. 

In  the  northern  part  of  the  Lava  ]\Iountains.  about  two  miles  from 
the  eastern  border  of  the  nuip,  a  single  bed  of  light-brown  translucent 


—  45  — 

chert  was  observed  interbedded  in  sandstones.    Tlie  bed  was  some  three 
feet  in  thickness  and  sliowod  a  well-developed  banding. 

Although  depositional  banding  may  commonly  be  observed,  especially 
in  the  sandstones*,  many  of  the  beds,  including  practically  all  the  days 
and  heavier  conglomerates,  are  quite  massive  and  offer  little  evidence 
of  the  structure. 

Weathering. 

The  general  softness  of  the  beds  makes  them  easily  eroded  by  the 
intermittent  streams  of  the  region.  The  action  of  the  streams  has  been 
chiefly  downeutting  with  the  resulting  development  of  canyons  bordered 
by  steep  cliffs  which  have  been  more  or  less  modified  in  form  by  rain 
wa.sh  and  wind  action.  Hence  in  many  parts  of  the  quadrangle 
excellent  exposures  of  Rosamond  strata  are  obtainable.  Such  exposures 
are  especially  well  developed  in  the  northern  part  of  the  Lava  Moun- 
tains. 

Where  stream  action  has  been  less  intensive  the  softness  of  the  beds 
has  resulted  in  but  poorly  developed  exposures.  The  lower  slopes  of 
Red  ^Mountain  show  such  poor  exposures,  but  higher  up  the  slope, 
immediately  below  the  contact  with  the  lavas,  sapping  action  has 
resulted  in  many  good  outcrops  which  are  scattered  on  all  sides  of  the 
mountain.  This  same  sapping  action  aided  by  the  steepness  of  the 
upper  slopes  of  the  mountain  has  resulted  in  covering  much  of  the  lower 
slopes  with  a  coating  of  lava  boidders  whicli  in  places  are  so  thick  as  to 
sti'ongly  resemble  lavas  in  place. 

Structure  and  Thickness. 

The  poor  exposures  over  much  of  the  area  where  the  Rosamond  beds 
outcrop,  aided  by  the  lava  talus  which  in  many  places  covers  the  sur- 
face and  by  the  massive  nature  of  many  of  the  beds  of  the  Rosamond 
series,  makes  any  exact  statement  of  the  structure  impossible. 

It  is  known  that  the  strata  are  rather  highly  folded  into  somewhat 
complex  folds  and  probably  more  or  less  faulted.  In  the  northern  part 
of  the  Lava  ^Mountains  the  beds  overlie  and  dip  away  from  the  quartz 
monzonite  at  angles  of  about  twenty-five  degrees.  In  a  short  distance 
they  pass  into  comiplex  folds  in  which  the  beds  may  possess  any 
attitude  from  horizontal  to  vertical. 

A  mile  west  of  Summit  Diggings  a  small  overturned  synclinal  fold 
was  observed  in  which  the  strata  passed  from  a  dip  of  twenty  degrees 
north  to  an  overturned  dip  of  about  eighty-five  degrees  to  the  north 
\nthin  a  distance  of  less  than  200  feet. 

In  the  vicinity  of  Red  ^fountain  the  structure  appears  to  be  equally 
complex.  In  the  region  from  a  mile  to  two  miles  east  and  southeast  of 
Johannesburg  the  strata  dip  to  the  southwest  at  an  angle  of  twenty 
degrees.  A  mile  further  south  they  lie  flat.  A  mile  south  of  Johannes- 
burg the  strata  dip  to  the  northeast  at  angles  of  from  ten  to  twenty 
i  degrees.  Seemingly  there  is  a  closed  synclinal  basin  developed  here 
which  centers  about  two  miles  southeast  of  Johannesburg.  At  the  time 
of  tliis  \^Titing  the  Big  Four  shaft  which  appears  to  lie  near  the  center 
of  this  depression  had  reached  a  depth  of  1100  feet,  all  in  beds  of  the 
Rosamond  series.  At  the  bottom  of  the  shaft  what  appeared  to  be 
I  lines  of  stratification  showed  a  dip  to  the  west  of  fifty -five  degrees. 


I 


—  46  — 

Whether  this  basin  is  the  result  of  folding  alone,  or  whether  faulting 
has  been  an  important  factor  in  its  development  is  not  known.  ^i 

"While  post-Rosamond  folding  has  certainly  occurred,  there  is  evidence™ 
that  folding  and  faulting  were  in  progress  during  the  deposition  of  the 
strata.  It  has  already  been  stated  that  rhyolitic  and  diabasic  rocks 
which  are  known  to  be  intrusive  into  the  lower  portion  of  the  series  are 
found  at  higher  horizons  incorporated  in  the  Rosamond  as  detrital 
material.  This  result  could  only  have  come  about  through  contem- 
poraneous folding  which  elevated  material  which  had  just  been 
deposited,  allowing  its  erosion  and  re-incorporation  in  strata  still  being 
deposited. 

Furthermore  the  silver  mineralization  is  knowji  to  have  occurred 
during  the  deposition  of  the  Rosamond.  And  yet,  the  silver  deposits 
are  cut  by  inter-mineralization  faults  which  must  also  have  effected  the 
Rosamond  beds. 

Manifestly  where  the  conditions  of  deposition  are  so  involved  and 
where  the  exposures  are  so  poor  no  exact  figures  can  be  given  for  the 
thickness.  It  seelns  probable  however  that  the  maximum  thickness  of 
the  Rosamond  strata  within  the  quadrangle  does  not  exceed,  although 
it  probably  approaches,  1000  feet.  The  depth  of  material  already  found 
in  the  Big  Four  shaft  is  largely  the  result  of  sinking  diagonally  through 
the  highly  inclined  strata. 

Relations  to  Adjacent  Formations. 

The  Rosamond  series  is  distinctly  younger  than  and  overlies  all  of 
the  formations  previously  described.  It  is  contemporaneous  in  part 
with  certain  rhyolitic  and  diabasic  intrusives.  And  it  is  older  than 
the  Red  Mountain  andesites.  The  material  composing  the  Rosamond 
appears  to  have  been  derived  very  largely  from  the  quartz  monzonites 
and  schists  found  within  the  region.  The  relation  between  the  Rosa 
mond  series  and  the  Red  Mountain  andesites  is,  in  general,  one  of 
angular  unconformity.  This  is  especially  true  in  the  northern  portion 
of  the  Lava  Mountains,  where  the  sedimentary  beds  may  at  times  stand 
vertically  beneath  the  lava  flows.  Immediately  beneath  the  contact 
with  the  lavas  on  the'  northwest  side  of  Red  Mountain,  the  Rosamond 
beds  dip  twenty  degrees  to  the  south  or  southwest,  while  the  contact 
dips  five  degrees  to  the  east. 

About  two  miles  further  south  on  this  same  contact,  however,  the 
Rosamond  strata  are  flat  and  appear  to  grade  upward  through  tuffaceous 
phases  into  the  overlying  lava  series. 

Thus  over  most  of  the  region  there  appears  to  be  a  definite  bre'ak 
between  the  two  groups  with  locally  a  gradation.  This  can  be  explained 
only  by  contemporaneous  folding  accompanied  by  erosion  of  the  crests 
of  the  folds,  the  eroded  material  being  deposited  in  the  adjacent  troughs 
of  the  folds,  and  by  the  absence  of  any  time  bre'ak  between  the  Rosa- 
mond series  and  the  Red  Mountain  andesites.  The  unconsolidated 
nature  of  the  Rosamond  beds  would  lend  itself  readily  to  an  action 
such  as  that  postulated,  so  readily  in  fact,  that  the  upper  surface  of  the 
Rosamond  during  its  later  history  might  be  expected  to  approach  the 
condition  of  a  peneplained  surface  without  any  break  in  sedimentation 
of  the  down-folded  (or  do\vn-faulted)  troughs  having  occurred.  Such 
a  surface  is  found  off  the  map  to  the  east  and  northeast,  where  the 


—  47  — 

upper  surface  of  the  Rosamond,  which  thou<:li  ohler  tlian  the  lava  flows 
has  here  never  been  covered  with  them,  is  quite  flat  though  now  tilted. 

Conditions  of  Accumulation. 

The  types  of  sediments  occurring  in  the  Rosamond  series  within  this 
quadrangle  as  well  as  the  structural  features,  permit  of  only  one  mode 
of  origin — namely,  accumulation  in  intermittent  lake  basins  in  an  arid 
climate.     The  deposition  may  have  been  in  part  subaerial. 

The  freshness  and  angularity  of  the  feldspars  and  the  presence  of 
biotite  and  ferromagnesian  minerals  in  these  sediments,  testify  to  the 
slight  degree  of  weathering,  the  short  transportation  undergone  and 
to  the  rapid  deposition.  The  slight  alteration  observed  in  such  easily- 
altered  minerals  could  only  result  from  erosion  in  an  arid  climate  such 
as  that  which  now  exists  in  the  region.  The  presence  of  the  gypsum 
is  best  explained  by  precipitation  in  shallow  waters  as  the  result  of 
evaporation.  The  gypsum  is  further  evidence  of  the  aridity  of  the 
Rosamond  climate. 

The  fairly  well-sorted  and  well-bedded  nature  of  certain  of  the  strata 
is  indicative  of  aqueous  deposition,  while  the  presence  of  beds  of  clay, 
chert  and  limestone,  bears  evidence  that  still  water  conditions  existed 
such  as -those  which  might  be  expected  in  a  lake.  In  contrast  to  these 
are  those  horizons  which  show  a  massive  heterogeneous  mixture  of 
boulders,  gravels  and  sands.  Such  horizons  may  be  subaerial  deposits 
in  part,  the  result  of  accumulations  of  flood  waters. 

During  the  period  intervening  between  the  intrusion  of  the  quartz 
monzonite  and  the  deposition  of  the  basal  beds  of  the  Rosamond,  this 
i-egion  appears  to  have  possessed  a  Avell-developed  drainage  system, 
for  during  this  interval  not  only  was  the  land  surface  reduced  to  one 
of  low  relief,  but  all  the  products  of  erosion  (which  must  have  repre- 
sented a  tremendous  quantity  of  resulting  sediments)  were  completely 
removed  from  the  region. 

The  lakes  in  which  the  Rosamond  strata  were  deposited  were  the 
residt  of  faulting  and  w\irping  wliich  destroyed  the  pre-existing  drain- 
age system  and  created  enclosed  ])asins  in  which  sedimentation  began. 
These  movements  did  not  cease  with  the  formation  of  the  basins  and 
the  inception  of  the  Rosamond  sedimentation,  but  continued  for  a  long 
period.  This  is  shown  by  the  incorporation  within  the  Rosamond  strata 
of  fragments  of  contemporaneous  intrusive  igneous  rocks — the  rhj^olites 
and  diabases.  It  is  further  shown  by  the  presence  of  detrital  gold  in 
the  tungsten  placers  near  Atolia  overlying  the  quartz  monzonite  and 
in  the  basal  beds  of  the  Rosamond  series  of  that  part  of  the  area.  This 
gold  was  without  doubt,  derived  from  the  region  a  few  miles  to  the 
north  where  it  is  known  to  be  later  than  the  basal  Rosamond.  Seem- 
ingly, the  basal  Rosamond  beds  near  Atolia  are  much  later  than  the 
basal  beds  exposed  south  of  Johannesburg.  The  localization  of  these 
basins  of  deposition  is  indicated  by  the  derivation  of  much  of  the 
material  from  the  immediate  vicinity. 

Age  and   Correlation  with  the   Rosamond  Series  of  Adjacent   Regions. 

No  fossils  were  found  within  the  Rosamond  series  in  the  Randsburg 
quadrangle.  On  the  basis  of  correlation  with  strata  in  adjacent  parts 
of  the  desert,  however,  the  age  is  determined  to  be  Upper  Miocene. 


—  48  — 

Til  the  type  section  near  Rosamond,  1650  feet  of  strata  occur  con- 
sistinji"  chiefly  of  p-ranitic  detritus  but  with  much  rhyolitic  tuff  at 
certain  horizons.  Two  rhyolite  flows  occur  interbedded  in  the  series, 
one  100  feet  thick,  750  feet  from  the  base,  the  other  300  feet  thick, 
1250  feet  from  the  base.  Recurrent  outcrops  of  these'  lavas  occur  to 
the  westward,  finally  passing'  beneath  Pliocene  sediments  near  the 
west  end  of  Antelope  Valley.^ 

North  of  Barstow,  in  the  Barstow  Syncline,  arkosic  and  tuffaceous 
sediments  occur  overl3ang  an  acid  basalt  or  a  basic  andesite,  fragments 
of  which  occur  in  the  overlying  sediments.-  These  beds  are  known 
from  their  fossil  content  to  be  Upper  Miocene  in  age.'' 

The  Ricardo  beds,  exposed  in  Redrock  Canyon  which  cuts  across  the 
El  Paso  Mountains  eighteen  miles  west  of  Randsburg,  consist  of  arkosic 
and  tuffaceous  sediments  which  are  very  late  Miocene  to  early  Pliocene.* 

The  beds  in  j^art,  overlie  intrusions  of  quartz  porphyry  (rhyolite?) 
and  diorite  porphyry  (diabase?).  Two  basalt  flows  separated  by  fifty 
feet  of  sediments,  occur  near  the  center  of  the'  series,  while  at  Black 
Mountain,  five  miles  west  of  the  northwestern  corner  of  the  Randsburg 
Qiiadrangle,  the  series  is  unconformably  overlain  by  thin  flows  of 
olivine  basalt.^ 

It  seems  probable  that  the  igneous  sequence'  during  the  Tertiary  has 
been  similar  over  a  limited  portion  of  this  part  of  the  Mojave  Desert. 
Thus  the  rhyolites  of  the  type  section  at  Rosamond  are  believed  to  be 
equivalent  to  the  rhyolitic  intrusions  near  Randsburg,  Avhile  the  basalt 
underlying  the  Barstow  syncline  may  be  the  equivalent  of  the  diabase 
of  this  area.  Similarly  the  quartz  porphyry  and  diorite  porphyry 
which  underlie  the  Ricardo  section,  may  be  the  equivalent  of  these  same 
rocks. 

The  basalt  flows  of  Black  Mountain  are  correlated  with  the  basic 
intrusives  of  the  northern  part  of  this  quadrangle.  These  are  uncon- 
formably younger  than  the  Red  oMountain  andesites.  Hence  the  andes- 
ites  which  are  of  a  basic  type,  may  be  the  equivalents  of  the  basalts 
which  occur  interbedded  in  the  Ricardo  section. 

If  this  reasoning  be  true,  the  Rosamond  series  represented  in  the 
Randsburg  quadrangle,  would  be  somewhat  older  than  the  Ricardo 
beds  and  more  or  less  equivalent  to  the  beds  at  Rosamond  and  those 
of  the  Barstow  Syncline,  or  in  other  words,  their  age  would  be  Upper 
Miocene. 

RHYOLITE-LATITE  SERIES  OF  INTRUSIVES. 

Shallow  intrusive  igneous  rocks  of  acid  composition  are  of  quite  wide- 
spread occurrence  in  the  Rand  Mountains.  The  intrusions  may  take 
a  variety  of  forms,  including  pipes,  dikes  and  sills.  These  are  known 
to  intrude  the  lower  beds  of  the  Rosamond  series,  while  detrital  frag- 
ments of  the  same  intrusives  are  found  higher  in  thatseries.     These 

'C.  L.  Baker.  Notes  on  the  Later  Cenozoic  History  of  the  Mojave  Desert  Region 
Univ.   Calif.    Bull.   Dept.   Geol.,   Vol.    6,    (1911),   pp.    333-383. 

=C.  Li.  Baker.     Op.  cit. 

'J.  C.  Merriam.  A  collection  of  Mammalian  Remains  from  Tertiary  Beds  in  the 
Mojave  Desert.     Univ.  Calif.  Bull.  Dept.  Geol.,  Vol.  6   (1911),  pp.  167-169. 

New  Protohippine  Horses  from  Tertiary  Beds  on  the  Western  Border  of  the 

Mojave   Desert.      Univ.    Calif.    I'.uII.    Dept.    Geol.,   Vol.    7    (1912),   pp.    435-441. 

■•J.  C.  Merriam.     Op.  cit. 

C.  L.  Baker.     Op.  cit. 

=C.  L.  Baker.  Physiography  and  Structure  of  the  Western  El  Paso  Range,  and 
the  Southern  Sierra  Nevada.     Univ.  Calif.  Bull.  Dept.  Geol.,  Vol.  7   (1912),  pp.  117-142. 


PLATE    IS 


k:^f*'f:  "^ 


A.    ROSAMOXIJ    SA.Xl  )SI(  ).\K.    i^=:  quartz.        :!((    ilia.       Ordinary    light. 


■^&m  :w^  f£\m 


-ik^r  -  ^  i^ 


^'r 


B.  RHYOLITK.  Q  rrr  quartz  phenocrysts ;  M  =  altered  muscovite ; 
groundmass  is  a  fine  granular  intergrowth  of  quartz  and  orthoclase. 
50   dia.       X  nicols. 


37841— facing  p.  48. 


—  49  — 

igneous  intrusives  therefor  are  of  the  same  age  as  the  lowei*  part  of 
the  Rosamond  series. 

The  occurrence  of  these  intrusive  rocks  is  practically  confined  to  the 
Rand  ^Mountains,  althouirh  certain  rhyolites  in  the  North  Rand  District 
north  of  Red  Mountain  (not  mapped),  probably  belong  to  the'  same 
group.  There  is  also  a  suspicion  that  dikes  of  this  series  may  occur  in 
the  vicinity  of  St.  Elmo  for  although  none  were  seen,  abundant  rhyolitic 
fragments,  some  of  good  size,  occur  in  that  neighborhood. 

Outside  of  this  area,  dikes  possessing  the  same  features  and  j^robably 
the  correlatives  of  those  here  d&scribed,  are  known  to  occur  at  Fremont 
Peak  and  in  the  vicinity  of  the  Silver  Dome  Mine,  fifteen  miles  to  the 
southeast. 

The  largest  of  the  many  intrusive  masses  is  a  pipe  which  forms  the 
major  portion  of  the  rugged  hill  a  mile  southeast  of  Johannesburg.  The 
dikes  Avithin  a  radius  of  three  miles  of  this  pipe  show  a  rough  radial 
arrangemejit  with  respect  to  it  which  suggests  a  very  close  relationship 
betweeii  the  dikes  and  the  pipe. 

The  dikes  find  their  major  development  in  the  region  within  two 
miles  of  Randsburg.  These  dikes  are  of  all  sjzes.  Many  were  observed 
which  had  a  thickness  of  only  a  few  inches.  Others  were  from  fifty  to 
a  hundred  feet  in  thickness.  Tlie  majority  would  probably  be  between 
two  and  ten  feet.  The  longest  of  the  many  dikes  is  about  a  mile  and 
a  half  in  length,  ruiniing  from  the  top  of  the  first  hill  west  of  the  pipe 
described  above  almost  to  the  Yellow  Aster  Mine.  This  dike  is  about 
twenty  feet  in  thickness.  ]V[ost  of  the  dikes  mapped,  however,  are'  only 
a  few  hundred  feet  to  a  few  hundred  yards  in  length.  These  short 
dikes  are  considoi'ed  by  the  writer  to  be  short  faulted  segments  of  what 
were  originally  longer  continuous  dikes.  Great  numbers  of  these  short 
segments  occur  which  were  not  mapped. 

Little  distinction  exists  between  the  dikes  and  the  sills  except  that 
the  latter  have  been  inti-nded  along  the  planes  of  schistosity  of  the  Rand 
schist.  The  mo.st  prominent  development  of  sills  in  the  region  was 
found  three-fourths  of  a  mile  east  of  Sidney  Peak. 

Both  the  dikes  and  sills  show  sharp  and  well-defined  contacts  with 
the  intruded  rocks.  Chilled  borders  are'  usually  to  be  observed  along 
the  contacts  of  the  intrusive.  Fragments  of  the  intruded  rocks  are 
occasionally  found  in  the  dikes  and  sills  but  are  by  no  means  common. 

Petrology. 

The  common  features  of  this  group  of  rocks  are  the  general  porphy- 
ritic  habit,  the  fine-grained  to  glassy  groundmass  and  the  liglit  color. 
The  phenocrysts  while  usually  prominently  developed  are  generally 
small.  P'eldspars  are  the  most  characteristic  phenocrysts,  usually  show- 
ing well-developed  cleavage  faces  and  good  crystal  outlines,  although  in 
some  cases  observed,  they  were  somewhat  rounded.  For  the  most  part 
they  show  no  albite  twinning.  Quartz  phenocrysts  are  quite  character- 
istic of  many  of  the  rocks,  either  as  i-ounded  grains  or  as  well-developed 
crystals  with  pyramidal  terminations  on  either  end.  The  quartz  though 
usually  colorless,  is  in  some  cases  smoky.  Some  of  the  dikes  show  a 
rather  strong  development  of  biotite  and  some  hornblende;  in  other 
occurrences  the  ferromagnesian  minerals  are  entirely  absent.  It  is 
only  in  specimens  from  the  larger  dikes  that  the  groundmass  can  be 
resolved  with  a  hand  lens,   in  most  cases  being  microervstalline  to 

4—37841 


—  50  — 

aphanitic.  More  rarely  the  groiindmass  may  be  glassy  when  it  may 
show  a  well-developed  flow  structure.  The  color  of  the  groundmass, 
and  hence  the  color  of  the  resulting  rock,  is  usually  a  light  gray,  white 
or  cream,  though  with  an  increase  in  the  visible'  content  of  biotite  and 
hornblende  the  groundmass  may  become  much  darker  in  color.  Where 
the  groundmass  is  glassy  the  rocks  appear  darker  in  color  than  where 
the  groundmass  is  crystalline.  A  mile  and  a  half  northeast  of  Osdick 
a  small  pipe  of  this  series  which  is  not  over  twenty  feet  in  diameter, 
is  intruded  into  the  Rosamond  strata.  The  rock  of  this  pipe  is  a 
vitreous  black  glass  which,  however,  is  quite  transparent  even  in  moder- 
ately thick  flakes. 

In  composition,  the  rocks  of  this  series  were  determined  microscopi- 
cally to  vary  from  rhyolites  through  trachytes  and  quartz  latites  to 
latites.  A  few  of  the  dikes  may  even  have  the  composition  of  andesites. 
The  average  composition  would  approximate  that  of  an  acid  quartz 
latite. 

Microscopically  the  more  acidic  rocks  were  found  to  be  practically  free  from 
magnetite  or  any  of  the  ferromagnesian  minerals.  Many  of  the  rhyolites  were  found  to 
consist  solely  of  orthoclase  and  quartz  in  varying  proportions,  possibly  with  traces  of 
muscovite.  These  rocks  are  practically  white  in  color.  With  the  addition  of  plagio- 
clases  a  small  quantity  of  ferromagnesian  minerals  aj^pear  also.  The  only  plagio- 
clase  observed  had  the  composition  of  an  acid  oligoclase,  while  the  iron-bearing 
minerals  included  brown  biotite,  green  hornblende,  magnetite  and  pyrite.  Apatite 
was  also  observed. 

An  especially  interesting  rock  type  was  found  in  the  east  end  of  the  dike  which 
terminates  at  the  top  of  the  first  hill  west  of  the  large  rhyolite  pipe.  This  rock, 
pure  white  in  color,  appeared  to  be  porphyritic  in  the  hand  specimen,  phenoci'ysts  of 
orthoclase  and  quartz  of  moderately  small  size  being  set  in  a  finely  crystalline 
groundmass.  Under  the  microscope  however  the  'groundmass'  was  found  to  consist 
of  orthoclase  crystals  of  approximately  the  same  size  as  the  phenocrysts,  each  of 
these  orthoclase  crystals  showing  a  well-developed  vermicular  intergrowth  with 
quartz.  The  quartz  intergrown  in  each  orthoclase  crystal  possessed  a  common 
orientation ;  that  in  adjacent  crystals  was  oriented  differently.  The  phenocrysts 
were  quite  clear  and  free  from  any  trace  of  intergrowth.  IMuscovite  in  traces  was 
the  only  other  mineral  present. 

A  number  of  intersections  of  dikes  of  this  series  were  observed  in 
thef  field.  Wherever  these  dikes  intersected,  it  was  observed  that  the 
more  basic  and  darker-colored  dike  cut  through  the  more  acid  and 
lighter-colored  one.  Seemingly,  the  intrusion  of  the  dikes  of  this  series 
was  a  slow  enough  process  that  one  dike  could  be  injected  and  solidify 
and  new  fractures  be  formed  before  the  injection  of  the  next  later  dikes, 
Seemingly  ' also,  the  magmatic  source  of  the  material  was  becoming 
slightly  more  basic  as  time  elapsed. 

Effects  on  Intruded  Rocks. 

Intrusions  of  rocks  of  this  rhyolite-latite  series  are  known  to  occur 
in  the  Johannesburg  gneiss.  Rand  schist,  Atolia  quartz  monzonite  and 
the  Rosamond  series.  In  the  vast  majority  of  cases,  the  intrusion  has 
had  no  effect  on  the  intruded  rock  so  far  as  can  be  told.  In  a  few  cases, 
however,  the  effects  on  the  intruded  rocks  are  noteworthy. 

Strata  of  the  Rosamond  series  surrounding  the  large  rhyolite  pipe 
lying  southeast  of  Johannesburg  have  been  highly  silicified  as  the  result 
of  the  intrusion,  the  silicification  apparently  being  the  result  of  hydro- 
thermal  activity.  On  the  north  the  silification  continues  out  as  far  as 
the  floor  of  the  valley,  while  on  the  west  all  of  the  Rosamond  strata 


PLATK   14. 


A.  RHYOLITB  WITH  VERMICULAR  INTERGROWTH.  Q  =  quartz 
phenocrysts ;  groundmass  composed  of  crystals  of  orthoclase  (black) 
showing  a  vermicular  interarowtli  of  quartz  (white).  50  dia.  X 
nicols. 


<■■•  -■'"•',' 


BASALT.  From  dike  of  L'pper  Miocene  age.  A  =  augite  ;  H  =  horn- 
blende ;  groundmass  consists  of  lath-shaped  crystals  of  labradorite 
set  in  a  light  brown  glass.    50   dia.    Ordinary  light. 


37841 — facing  p.   50. 


—  51  — 

exposed  are  hiprhly  silicified.  Near  the  saddle  on  the  contact  between 
the  Rosamond  beds  and  the  quartz  nionzonito,  the  ([uartz  monzonite 
itself  has  been  lii.i2:hly  altered  apparently  by  the  same  hydrothermal 
activity.  Where  they  have  been  hijihly  silicified  as  they  have  he're, 
the  arkosic  sandstones  of  the  Rosamond  series  become  extremely  hard 
so  that  they  break  throu<i:h  the  detrital  f rafjments,  jriving  fresh  feldspar 
cleavajje  faces  and  showing  flakes  of  ferromagnesian  minerals.  The 
resulting  rock  bears  a  very  strong  resemblance  to  a  granitic  rock. 

Tlie  intrusive  jnpe  is  not  in  itself  a  simple  intrusion,  but  has  broken 
up  llirough  the  sediments,  including  within  itself  large  blocks  of  this 
now  liigldy-silieified  sandstone,  so  that  the  rliyolite  exposure  as  mapped 
is  in  reality  a  complex. 

About  two  miles  northeast  of  this  large  pipe  two  smaller  ones  occur, 
also  intrusive  into  the  Rosamond  series.  Although  these  two  snuill 
pipes  are  only  from  ten  to  twenty  feet  in  diameter  they  are  each  sur- 
rounded by  an  aureole  of  silicified  sediments  several  hundred  feet  in 
diameter.  The  southernmost  of  these  two  occurrences  stands  out  prom- 
inently as  a  round  white  knoll  on  the  northwest  side  of  Red  Mountain. 
The  sediments  here  intruded,  consist  chiefly  of  clays  and  some  tutfa- 
ceous  material.  These  have  been  hardened  to  a  white  resistant  rock 
which  bears  a  strong  resemblance  to  a  light  colored  lava. 

A  similar  silicification  of  the  Rosamond  series  adjacent  to  rhyolitic 
intrusions  is  to  be  observed  in  the  North  Rand  District  just  south  and 
southeast  of  Mountain  Wells. 

The  silicification  which  has  followed  the  intrusion  of  the  rhyolites 
in  the  cases  described  is  believed  to  be  the  result  of  hydrothermal 
activity,  the  solutions  and  silica  being  of  magmatic  origin.  The  solu- 
tions accompanying  or  following  the  intrusions  have  had  little  effect 
where  the  wall  rocks  were  solid,  but  as  soon  as  the  porous  sediments 
of  the  Rosamond  series  were  entered  the  solutions  spread  out  depositing 
their  burden  of  silica.  The  strong  resemblance  of  the  rhyolite  possess- 
ing the  marked  development  of  the  vermicular  intergrowth,  both  in 
composition  and  texture  to  what  might  be  expected  should  a  pegmatitic 
ditTerentiate  approach  the  earth's  surface  would  be  in  strict  accord  with 
the  idea  of  magmatic  origin  of  these  solutions. 

The  possibility  of  the  silification  being  the  result  of  intrusion  of  the 
rhyolitic  magma  into  wet  sediments  underlying  a  Miocene  lake,  with 
resulting  interaction  between  the  magma  and  water  must  not  be  over- 
looked. It  is  felt  that  this  possibility  can  be  ruled  out,  however,  due  to 
the  presence  in  the.se  silicified  zones  of  a  noticeable  though  spotted  gold 
and  silver  content.  Gold  and  silver  are  practically  absent  from  the 
Rosamond  sediments  in  general,  as  shown  b}'  assays  of  samples  of  these 
sediments  taken  from  various  prospect  shafts.  Hence  the  presence  of 
gold  and  silver  in  these  silicified  zones  appears  to  be  explainable  only 
on  the  assumption  that  the  solutions  responsible  for  the  silicification 
were  of  magmatic  origin. 

Age. 

As  has  already  been  indicated  in  discussing  the  Rosamond  series, 
the  rhyolite-latite  series  intrudes  the  lower  beds  of  the  Rosamond  series, 
while  detrital  fragments  of  these  intrusives  are  found  incorporated 
within  the  Rosamond  at  higher  horizons.  The  large  rhyolite  pipe  is 
estimated  to  intrude  approximately  the  lower  two  hundred  feet  of  the 


—  52  - 

sediments,  while  rhyolite  pebbles  were  found  in  the  small  hill  just  south 
of  the  Fox  Lease  shaft  at  a  horizon  which  eonld  not  be  mncli  more  than 
two  hundred  feet  above  the  base  of  the  Rosamond.  The  rhyolite-latite 
intrusives  occurred  tlien,  when  about  200  feet  of  Rosamond  strata  had 
accumulated  and  their  ages  would  be  approximately  early  Upper 
Miocene. 

Weathering. 

The  rocks  of  the  rhyolite-latite  series  are  f|uite  resistant  to  the  arid 
erosion  of  this  region  and  hence  usually  stand  out  conspicuously  on  the 
surface.  The  hill  southeast  of  Johannesbur<>-  is  quite  rugjjed  and  prom- 
inent by  reason  of  the  rhyolite  pipe  composing'  it.  The  dikes,  especially 
in  the  elevated  country  (juite  commonly  follow  alonp-  ridp'e  lines  and 
appear  to  have  been  an  i)nportant  factor  in  controlliuii'  the  position  of 
the  ridg-es.  Tn  the  flats,  dikes  are  commoidy  found  to  outcrop  wheli 
other  rocks  show  no  exposure  whatever. 

The  dikes  are  eroded  chiefly  by  the  breaking  out  along  joint  planes 
of  rather  angular  fragments,  more  or  less  rectangular  in  shape.  These 
fragments  commonly  cover  the  slopes  for  some  distance  below  the  out- 
crop of  a  dike. 

The  surface  of  the  dikes  is  usually  stained  a  yellow-brown  by  iron 
oxides.  This  same  discoloration  works  in  along  the  joint  planes  as 
well,  staining  the  rock  for  a  distance  of  a  half  an  inch  or  more  from 
each  fracture.  The'  soil  adjacent  to  the  dikes  is  quite  commoidy  stained 
the  same  brown  color,  so  that  at  times  when  no  dike  is  exposed,  its 
presence  may  be  inferred  by  the  discoloration  of  the  soil. 

DIABASE— BASALT  SERIES  OF  INTRUSIVE. 

Dark-colored  basic  dikes  having  the  composition  and  texture  of 
either  a  (lial)ase  or  a  basalt  are  much  more  common  in  the  Randsburg 
quadrangle  than  would  be  indicated  by  the  mapping.  Although  only 
a  few  dikes  were  observed  whicli  were  large  enough  to  map ;  dikes  of 
this  gi"ou]i  were  found  underground  in  nine  different  mines  of  the 
region  and  are  known  to  occui'  in  at  least  seven  others,  either  through 
finding  diabase  fragments  on  tlie  dumps  of  these  mines  or  through 
second-hand  information. 

Field  Relations. 

The  areal  distribution  of  This  series  of  dikes  appears  to  be  roughly 
the  same  as  the  distribution  of  the  rhyolite-latite  series.  They  were 
observed  in  various  parts  of  the  Rand  ■Mountains.  Fragments  of 
diabase  were  picked  up  on  the  dump  of  the  North  Rand  ^Mine,  southeast 
of  ^fountain  Wells,  and  also  on  the  dump  of  the  I'nion  Mine  at  Atolia. 
Outside  of  the  quadrangle,  similar  dikes  are  known  at  Fremont  Peak 
and  at  the  Silver  Dome  ^line. 

In  addition,  certain  strongly  porphyritie  dikes  having  the  composi- 
tion of  hornblende-hypersthene  diabase  which  are  found  in  the  region 
southeast  of  the  El  Paso  Peaks  probably  belong  to  this  series.  Because 
of  lack  of  time  in  the  field,  the^e  last  dikes  were  not  mapped. 

The  dikes  vary  considerably  in  size.  The  largest  known  in  the 
region  is  a  mile  and  a  half  in  length  and  from  twenty  to  fifty  feet  in 
thickness.  This  is  the  dike  passing  through  the  Butte,  Kenyon,  Wedge 
and  Little  Butte  mines. 


—  53  — 

The  dikos  observed  imderjrround  were  usually  small,  varying  in 
thickness  from  a  few  inches  up  to  ten  feet.  For  the  most  ]iart,  thes(> 
smaller  dikes  tliou<ili  possessing  sharp  walls,  are  quite  irregular  in 
habit,  the'  fissures  into  wliich  they  were  injected  being  neither  prominent 
nor  persistent. 

Intersections  of  these  diabase  or  basalt  dikes  witli  dikes  of  the 
rhyolite-latite  series  were  observed  in  a  numl)er  of  places,  as  for 
example,  along  the  large  dike  mentioned  as  passing  through  the  Butte 
^fine.  In  every  case  the  rhyolite-latite  dike  was  cut  by  the  diabase  or 
basalt  dike. 

These  diabase  and  basalt  dikes  are  known  to  intrude  the  Rand  schist, 
the  quartz  monzonite.  the  rhyolite-latite  series  and  the  Rosamond  series. 

In  the  small  hill  just  south  of  the  Fox  Lease  shaft  a  small  sill  and  a 
small  dike  of  diabase  occur  cutting  the  Rosamond  beds  at  a  horizon 
estimated  to  be  slightly  over  200  feet  above  the  base.  Each  of  these  is 
only  a  few  inches  in  thickness.  The  adjacent  Rosamond  beds  are  more 
or  less  silicified  and  cut  by  calcite  veinlets.  Subangular  fragments  of 
light-colored  porphyritic  rhyolite,  a  rhyolite  similar  in  all  respects  to 
that  intrusive  into  the  hill  to  the  northwest,  occur  incorporated  in  the 
sediments  adjacent  to  the  diabase.  Apparently  sufficient  time  had 
elapsed  between  the  intrusion  of  the  rhyolites  and  the  intrusion  of  the 
diabase  for  the  rhyolites  to  have  become  uplifted  and  subjected  to 
erosion.  The  silicification  of  the  Rosamond  beds  here  manifestly 
occurred  long  after  the  intrusion  of  the  rhyolites  and  hence  in  this 
case  the  silicification  pi-obably  represents  the  action  of  solutions  which 
accompanied  and  followed  the  diabasic  intrusions. 

Petrology. 

The  most  characteristic  feature  of  the  diabase-basalt  dikes  is  the 
high  content  of  ferromagne'sian  minerals  and  magnetite  and  the  conse- 
quent dai-k  color  of  the  rocks.  As  seen  in  the  field,  the  color  of  the 
rocks  may  be  almost  any  shade  of  dark  gray  to  black.  Sometimes  a 
greenish  tinge  is  noticeable. 

In  almost  every  case  observed,  the  rocks  were  holocrystalline,  although 
in  a  few  cases  of  very  small  dikes,  the  texture  was  i)orphyritic  with  an 
aphanitic  groundmass.  The  coarseness  of  the  crystallization  appears  to 
be  a  direct  function  of  the  size  of  the  dike.  Thus  the  diabase  of  the 
large  dike  already  mentioned  is  quite  coarse  grained.  The  diabasic 
texture  of  these  rocks  is  usually  most  ea.sily  observed  on  the  weathered 
surface  of  the  rock. 

The  diabases  as  studied  in  the  field,  were  found  to  be  composed  of 
well-developed  lath-shaped  crystals  of  plagioclase  feldspar  showing 
albite  twinning,  these  crystals  being  surrounded  by  dai-k  colored 
minerals,  which,  in  the  coarser  grained  rocks  could  be  identified  in 
part,  as  hornblende.  In  addition,  occasional  small  patches  of  pyrite 
were  usually  present.  The  felds])ar  might  make  up  any  proportion  of 
the  rock  up  to  fifty  per  cent  of  the  total  composition. 

Under  the  raicroscoi)e  the  feldspars,  present  as  well-developed  lath-shaped  crystals 
were  found  in  various  specimens  to  vary  in  composition  from  andesine  to  labradorite. 
Green  hornblende  and  augite  in  varying  proportions  occur  surrounding  the  feldspars. 
Magnetite  is  always  moderately  abundant,  while  in  a  few  cases  small  quantities  of 
what  appeared  to  be  primary  quartz  appeared.  Many  of  the  rocks  classed  in  the 
field  as  basalts  were  found  under  the  microscope  to  be  'micro-diabases.' 


-  54  -  .  5 

Practically  all  the  diabases  studied  showed  varying  degrees  of  alteration.  This 
alteration  is  first  apparent  by  the  saussuritisation  of  the  feldspars  with  the  develop- 
ment of  calcite  in  the  rock,  followed  by  the  alteration  of  the  ferromagnesian  minerals 
to  aggregates  of  chlorite  and  iron  oxides.  But  even  where  the  rock  has  been  fairly 
highly  altered  remnants  of  the  original  diabasic  texture  could  usually  be  made  out 
in  the  spacing  of  the  secondary  minerals. 

This  alteration  is  in  part  independent  of  surface  weathering,  for  diabases 
obtained  underground  at  depths  of  several  hundred  feet  were  commonly  badlj 
altered, — a  hydrothermal  alteration. 

The  basalts  are  usually  porphyritic  with  a  very-fine  crystalline 
groundmass.  Taken  as  a  whole  they  are  probably  slightly  finer  in  grain 
and  possibly  a  little  darker  in  color  than  are  the  diabases.  The  pheno-  \ 
crysts  can  be  identified  in  the  hand  specimen  as  consisting  largely  of 
feldspar  and  hornblende.  These'  phenocr^^sts  are  usualty  of  rather 
small  size.  ^ 

Under  the  microscope  the  feldspars  were  found  to  possess  the  composition  of  i 
labradorite.  Other  phenocrysts  consisted  of  short  stubby  crystals  of  brown  horn- 
blende and  occasional  crystals  of  augite.  The  groundmass  of  various  specimens  was 
found  to  consist  chiefly  of  minute  lath-shaped  crystals  of  labradorite  with  scattered 
grains  of  magnetite.  In  a  few  cases  part  of  the  groundmass  consisted  of  a  brownish 
devitrified  glass.  In  all  the  specimens  studied  there  appeared  to  be  a  very  notice- 
able tendency  towards  alteration  as  was  observed  with  the  diabases. 


The  dikes  found  in  the  region  southeast  of  the  El  Paso  Peaks  have 
a  striking  appearance  in  the  field  due  to  the  development  of  very  large 
phenocrysts  of  hornblende.  These  phenocrysts  are  commonly  well- 
formed  crystals  which  may  be  more  than  an  inch  across.  Other  small 
phenocrysts  of  plagioclase  and  of  a  light-green  mineral  are  rather  abun- 
dant. The  groundmass  is  very  fine  crystalline  and  rather  dark  in 
color. 

Under  the  microscope  the  feldspars  were  determined  as  labradorite,  while  the 
green  mineral  was  found  to  be  hypersthene.  The  groundmass  possessed  a  noticeable 
diabasic  texture  and  was  composed  of  about  fifty  per  cent  lath-shaped  labradorite 
crystals,  the  balance  being  chiefly  green  hornblende  with  lesser  amounts  of  hypersthene 
and  primary  quartz.  Magnetite  in  small  grains  was  sprinkled  liberally  through  the 
rock.     This  rock  should  properly  be  termed  a  hornblende-hypersthene  diabase. 

Weathering. 

The  diabases  and  basalts  appear  to  weather  quite  readily,  which  fact 
taken  in  conjunction  with  the  small  size  of  many  of  the  dikes  readily 
accounts  for  the  limited  number  seen  on  the  surface  as  compared  with 
the  number  observed  underground. 

The  surface'  portion  of  these  dikes  is  usually  weathered  to  a  light 
gray-colored  rock  which  is  more  or  less  stained  with  yellowish-broA^Ti 
iron  oxides.  The  rocks  at  the  same  time  appear  to  become  somewhat 
softened.  Thus  it  is  commonly  impossible  to  obtain  a  fresh  piece  of 
rock  from  the  outcrops  of  these  dikes. 

The  dikes  rarelj^  show  prominent  outcrops.  It  is  probable  that  many 
dikes  actually  reach  the  surface  but  are  obscured  by  detritus  from 
the  adjacent  more  resistant  rocks. 

Age. 

The  diabases  are  knowai  to  be  slightly  younger  than  the  rhyolite- 
latite  series  and  they  intrude  the  Rosamond  series  at  a  horizon  some- 
what higher  than  200  feet  from  the  base.    Detrital  diabase  fragments 


I 


1 


—  55  — 


appear  incorporated  in  the  Rosa- 
mond beds  at  still  higher  horizons. 
The  exact  horizon  at  which  they  first 
appear  is  not  definitely  known  but 
is  estimated  to  be  in  the  neighbor- 
hood of  five  hundred  feet  above  the 
base  of  the  Kosamond  in  the  vicin- 
ity of  Osdick.  The  age  of  the  dia- 
base-basalt series  then  would  be 
approximately  that  of  the  middle 
of  the  Rosamond  series  or  Upper 
Miocene. 

RED    MOUNTAIN   ANDESITE. 

Overlying  the  Rosamond  series, 
usually  with  angular  uncomformity, 
is  a  thick  series  of  igneous  rocks  con- 
sisting chiefly  of  lava  flows  but  with 
prominent  amounts  of  agglomerates 
and  tuffs.  The  general  composition 
of  this  series  is  that  of  a  basic 
andesite. 

Field   Relations. 

These  rocks  occur  as  a  thick  cap- 
ping o^  erlying  the  Rosamond  series 
in  Red  Mountain  and  over  most  of 
the  central  portion  of  the  Lava 
Mountains.  Further  north  in  the 
Lava  ^Mountains,  the  andesite  expos- 


PLATB  15. 


A.  RHYOLITE  DIKE.  Cutting  quartz 
monzonite  three-fourths  of  a  mile 
southeast  of  Randsburg. 


B.    RED     MOUNTAIN     FROM     THE     WEST.        L  =  lava     flows;     R --=  Rosamond 
series  ;  S  =  Rand  schist ;  QM  =  quartz  monozonite  ;  A  _  alluvium. 


—  56  — 

ures  become  isolated  patches,  due  in  part,  to  erosion  cutting  through 
the  flows  into  the  underlying  Rosamond  series,  and  in  part,  to  originally 
isolated  flows.  The  flows  in  this  part  of  the  region  have  overlapped 
in  places  on  the  quartz  monzonite.  The  large  area  of  lavas  east  of 
Summit  Diggings  rests  directly  on  the  quartz  monzonite  along  its 
eastern  border,  but  further  west  the  Rosamond  beds  appear  exposed 
by  erosion  from  beneath  the  center  of  the  flows.  North  of  the  Garlock 
Fault,  in  the  region  northwest  of  Summit  Diggings,  two  small  isolated 
patches  of  andesite  are  found  surrounded  by  quartz  monzonite,  while 
further  east  a  number  of  small  blocks  of  lava  are  found  in  direct  contact 
with  the  fault.  Former  extension  of  the  lavas  is  evidenced  by  their 
occurrence  in  an  irregular  exposure  three  miles  north  of  Johannesburg. 

The  great  resistance  of  these  lava  flows  to  erosion  favors  the  develop- 
ment oi^  excellent  exposures.  The  rocks  constituting  the  flows  are  ordin- 
arily quite  fresh  and  show  only  traces  of  weathering.  The  flows  tend  to 
form  prominent  topographic  features  with  steep  slopes.  These  steep 
slopes  appear  to  be  chiefly  the  result  of  sapping  action,  the  soft  under- 
lying Rosamond  beds  being  washed  out,  allowing  the  breaking  oft'  of 
large  blocks  of  the  overlying  lavas.  This  has  caused  the  development  of 
large  talus  slopes  and  steep  (in  some  cases  vertical)  cliffs. 

The  Lava  Mountains  show  a  fairly  flat  summit  which  appears  to 
represent  a  part  of  the  original  surface  of  the  flows.  This  surface  shows 
only  a  moderate  amount  of  dissection. 

It  is  believed  that  over  most  of  the  area  tlie  surface  of  the  Rosamond 
series  was  a  flat  even  plain  at  the  time  the  lavas  were  poured  out. 
Traces  of  this  plain,  now  tilted  to  the'  north,  which  largely  escaped  any 
cover  of  lava  flows,  are  found  to  the  east  of  the  northeast  corner  of  the 
quadrangle.  The  contact  between  the  lavas  and  the  underlying  sedi- 
ments on  the  north  side  of  Red  Mountain  when  viewed  from  a  distance, 
is  seen  to  be  an  even  surface  whicli  dips  to  the  east  at  an  angle  of  about 
five  degrees.  At  the  same  time  the  summit  line  of  Red  Mountain  is 
seen  to  roughly  parallel  this  lower  contact. 

Exceptions  to  this  flat  upper  surface  of  the  Rosamond  are  found  in 
the  northern  part  of  the  Lava  Mountains.  Here,  apparently  as  the 
result  of  an  uplift,  deep  canj^ons  had  been  dissected  before  the  lava 
extrusion.  These  canyons  appear  to  have  been  quite  similar  to  those 
which  now  exist.  This  dissection  was  apparently  controlled  by  the 
presence  of  the  hard  and  resistant  quartz  monzonite  adjacent  to  the 
soft  Rosamond  strata.  When  th^  lava  flows  appeared,  they  tended  to 
run  into  these  ancient  canyons,  either  partly  filling  them  or  where  the 
flow  froze  too  rapidly,  leaving  a  tongue  of  lava  on  the  side  slope  of  the 
canyon.  Many  of  these  tongues  of  lava  exist  today  apparently  in 
much  the  same  state  as  when  they  were  first  extruded.  A  good  example 
may  be  noticed  on  the  map  in  the  region  about  a  mile  and  three-quarters 
southwest  of  Bedrock  Spring. 

Mechanics  of  Extrusion. 

The  Red  Mountain  andesites  as  a  group  appear  to  be  the  result  of 
fissure  flows  on  a  small  scale.  Many  of  these  fissures  through  which  the 
molten  rock  was  erupted,  may  now  be  observed  in  the  field  as  dikes. 
A  few  such  dikes  were  observed  in  the  northern  part  of  the  Lava  Moun- 
tains, but  by  far  the  best  development  was  found  in  the  area  mapped  as 
Rosamond  series  on  the  east  side  of  Red  Mountain.     In  this  area  numer- 


—  57  — 

ous  dikes  were  observed  cutting  the  Rosamond  which  were  petrographi- 
cally  the  same  as  the  flows  and  apparently  passed  into  the  flows.  These 
dikes  are  of  various  sizes,  the  largest  observed  being  over  fifty  feet  in 
thickness  and  upwards  of  half  a  mile  in  length. 

These  dikes  have  had  no  apparent  effect  on  the  Rosamond  series 
where  they  cut  beds  of  that  group.  No  matter  whether  the  adjacent 
sediments  are  sandstones  or  clays,  they  remain  practically  unconsoli- 
dated right  up  to  the  contact  with  the  dike  so  that  they  may  be  pulver- 
ized by  the  pressure  of  ones  fingers.  It  is  believed  that  this  could  only 
result  if  the  magma  were  in  the  condition  of  a  dry  melt  at  the  time  of 
extrusion. 

While  many  of  these  fissure  flows  appear  to  have  been  of  a  quiet  type, 
the  abuiulance  of  pyroclastic  material  interbe'dded  with  the  lavas  shows 
that  explosive  action  was  jirominent  during  certain  periods  of  the 
extrusion.  Whether  this  explosive  activity  occurred  in  connection  with 
these  fissure  flows  or  whether  somewhere  within  this  area  true  central 
vents  existed,  is  not  known.  The  form  of  Red  Mountain  as  well  as  the 
excessive  thickness  of  lavas  developed  within  the  mountain  are  sugges- 
tive of  its  having  at  one  time'  been  the  site  of  such  a  central  vent. 

Petrology. 

The  lavas  of  this  group  are  quite  commonly  strongly  colored.  Many 
of  them  are  brownish-red,  reddish-brown,  buff,  reddish-purple  or  various 
shades  of  dark  gray.  Red  Mountain  derived  its  luime  from  the  strong 
develojnnent  within  it  of  brownish-red  lavas  which  give  the  mountain-a 
noticeable  reddish  color  when  viewed  from  a  slight  distance. 

These  rocks  are  usually  strongly  i)orphyritic  with  a  glassy  to  aphan- 
itic  groundmass.  The  abundant  phenocrysts,  many  of  which  are  of 
rather  large  size,  consist  chiefly  of  colorless  to  white  plagioclase  feldspar 
which  usually  shows  well-developed  albite  twinning.  These  feldspar 
phenocrysts  commonly  show  an  irregular  outline  as  though  they  had 
been  broken  or  resorbed.  Besides  the  feldspars,  biotite  and  hornblende 
are  commonly  observed  as  phenocrysts.  The  relative  proportions  of 
biotite  and  hornblende  vary  greatly  in  the  several  flows. 

Under  the  microscoix",  jrlass.v  and  mlcrocrysfallino  urnnnd  masses  were  both 
observed,  the  former  beinj?  tlie  more  al)iin(huit.  Those  which  were  glassy  varied 
from  colorless  to  light  brown  as  seen  in  thin  section.  Those  having  a  microcrystai- 
line  gronndmass  were  composed  of  tine  feldspar  laths  and  minute  scattered  grains 
of  magnetite.  The  phenocrysts  were  composed  most  frequently  of  feldspars,  followed 
in  order  of  abundance  by  green  hornblende,  basaltic  hornblende,  deep  brown  biotit?, 
augitc  and  hypersthene.  The  feldspars  usually  had  the  composition  of  a  basic 
labradoritc  (Ab3oAn-„),  but  variations  were  observed  from  andesine  to  bytownite. 
Zoning  was  commonly  developed  in  the  feldspars,  while  the  hornblendes  were  almost 
always  enveloped  by  a  strong  reaction  zone  of  magnetite. 

These  rocks  might  be  correctly  described  as  either  basic  andesites  or 
acid  basalts.  J.  E.  Spurr  has  correctly  designated  them  as  aleutites,^ 
but  due  to  the  less  common  usage  of  the  term  aleutite,  and  to  the  fact 
that  another  grou]>  of  rocks  occurs  in  the  quadrangle  possessing  the 
composition  of  basalts,  it  has  been  found  most  expedient  in  this  report 
to  adopt  the  term  Red  ^Mountain  andesite  for  this  group. 

Interbedded  with  the  lava  flows  which  constitute  the  major  portion  of 
the  series  are  important  beds  of  agglomerate  and  tuff.    The  agglomerates 

'i:  E.  Spurr.  U.  S  G.  S.  Bull.  208,  p.  216.  An  aleutite  Is  a  rOck  having  a  com- 
position intei-mediate  between  an  andesite  and  a  basalt. 


—  58  — 

are  composed  of  angular  fragments  of  lavas  similar  to  those  already 
described  which  are  imbedded  in  a  tiiffaceoiis  matrix.  The  fragments 
are  of  all  sizes,  many  of  those  observed  being  over  ten  feet  across.  The 
agglomerates  appear  to  be  especially  well  developed  near  tlie  base  of 
the  series.  The  tnffs  are  quite  commonly  white  in  color  although  some 
were  observed  wliich  were  pink  or  reddish-brown.  They  are  quite  tine 
in  grain  but  contain  small  scattered  f  ragmelits  of  lava  and  crystals  of 
feldspar,  biotite  and  hornblende.  Locally  within  the  quadrangle,  these 
tuffs  have  been  mined  for  an  abrasive. 

Occasional  inclusions  of  pebbles  from  the  Rosamond  series  are.  to  be 
found  within  the  lava  flows.  One  or  two  inclusions  of  schist,  similar 
in  all  respects  to  schists  of  the  Rand  series,  which  were  found  by  the 
writer  on  the  east  side  of  Red  Mountain  could  easily  be  mistaken  for 
evidence  of  underlying  schistose  rocks  by  one  not  familiar  with  the 
Rosamond  series. 

Structure  and  Thickness. 

These  lavas  have  been  little  effected  by  folding  since  they  were  orig- 
inally poured  out  on  the'  surface.  The  base  of  the  lavas  in  Red  Moun- 
tain is  a  flat  even  surface  which  dips  to  the  east  at  an  angle  of  five 
degrees.  This  dip  is  probably  the  result  of  slight  folding  in  the  region 
since  the  lavas  were  formed. 

The  lavas  have  been  effected  by  faulting,  being  involved  in  move- 
ments along  the  Garlock  Fault.  They  seem  to  be  effected  by  faulting 
also  in  the  region  north  of  Red  Mountain.  No  detailed  information 
was  obtained  concerning  the  position  and  extent  of  these  latter  faults. 

The  lavas  appear  to  reach  their  maximum  thickness  in  Red  Mountain 
where  approximately  1400  feet  of  flows  and  pyroclastics  exist.  It  is 
not  believed  that -erosion  has  reduced  the  original  thickness  to  any 
appreciable  extent.  The  maximum  thickness  in  the  Lava  Mountains 
appears  to  be  much  less,  being  in  the  neighborhood  of  850  feet,  while 
over  much  of  the  area  now  occupied  by  flows  the  original  thickness  was 
probably  only  a  few  hundred  feet. 

Age. 

The  Red  Mountain  andesites  are  probably  Pliocene  in  age,  being 
limited  by  the  Rosamond  series  of  the  quadrangle  below,  and  by  an 
unconformable  relation  to  the  Black  Mountain  basalt  (IMiddle  Pliocene 
to  Pleistocene)  above.  On  the  basis  of  correlation  with  the  basalt  flows 
which  occur  interbedded  in  the  Ricardo  section,  which  would  seem  to 
be  reasonable,  the  Red  IMountain  andesites  would  be  very  early 
Pliocene. 

BLACK   MOUNTAIN   BASALT. 

Basalts  of  this  group,  which  includes  both  intrusive  and  extrusive 
types,  are  only  found  in  this  area  in  a  few  small  occurrences  in  the 
north-central  part  of  the  quadrangle. 

Field   Relations. 

The  largest  of  these  occurrences  is  an  irregular  intrusive  pipe  wliich 
has  overflowed  on  the  surface.  The  basalt  is  now  exposed  over  an  area 
roughly  one-third  by  one-fourth  mile  which  lies  just  east  of  the  railroad 


PLATE   16. 


i  ^m 


^ 


'^S^-:^r.3JS/^SX  ^. 


1 


iv^'f 


A.  PYROXENE  AXDESITK  FROM  RED  MOUNTAIN.  L  -  labradorite  ; 
B  tir  biotite  ;  H  =  hornljlende  ;  A  rzr  augite.  The  groundmass  is  a 
light  brown  glass.    50  dia.    Ordinary  light. 


B.     SAME   .AS   "A"   BUT  WITH   CROSSED  NICOLS. 


37841— facing  p.  58. 


—  59  — 

a  half-mile  north  of  Summit  Dip:o:incrs.  Good  exposures  are  obtainable 
in  a  cut  made  in  buildiiifr  the  railroad. 

The  basalt  in  tliis  pipe  has  intruded  its  way  through  Rosamond 
strata  and  Red  Mountain  andesites  to  the  surface,  and  has  overflowed 
part  of  the  surrounding  surfacef,  covering  it  with  a  basalt  layer  about 
three  feet  in  thickness.  This  flow  was  largely  down  the  side  of  a  small 
canyon  which  existed  in  the  Red  ^Mountain  andesites  previous  to  the 
basalt  extrusion.  The  intrusive  pipe  appears  to  underlie  most  of  the 
area  mapped  as  basalt  in  this  occurrence. 

A  quarter  of  a  mile  to  the  northeast  two  other  small  occurrences  of 
basalt  were  noted,  tliougli  from  the  poor  exposures  it  could  not  be 
determined  whether  they  were  intrusive  or  outlying  remnants  of  the 
flow  above?  described. 

In  the  region  a  half  mile  northeast  of  Summit  Diggings,  two  small 
iiills,  one  on  either  side  of  the  county  road,  possess  a  capping  of  thin 
basalt  flows,  identical  in  appearance  and  composition  with  that  found 
along  the  railroad.  The  flow  in  the  southernmost  of  these  hills  is  only 
a  few  feet  thick,  the  flow  in  the  other  occurrence  being  much  thicker. 
Both  overlie  strata  of  the  Rosamond  series. 

It  is  believed  that  all  of  these  occurrences  are  remnants  of  a  flow 
derived  from  the  intrusive'  pipe  adjacent  to  the  railroad.  They  are  now 
found  in  isolated  patches  due  to  erosion  having  removed  the  intervening 
portions  of  the  flow. 

The  second  largest  exposure  of  basalt  is  at  the  head  of  Hardcash 
Gulch,  a  mile  and  a  half  west  of  Summit  Diggings.  The  mass,  from  its 
mapping  and  also  from  its  effect  on  the  surrounding  beds  of  the  Rosa- 
mond series  is  known  to  be  an  intrusive  pipe.  It  transgresses  the  bed- 
ding of  the  Rosamond  series  and  has  highly  silicified  the  sandstones 
and  clays  of  that  series  so  that  they  now  exist  as  hard  and  resistant 
rocks.  The  silicified  arkose  sands  with  their  fresh  feldspars  strongly 
re^semble  granitic  rocks.  This  silicification  persists  for  some  distance 
east  from  the  pipe  possibly  indicating  an  unexposed  extention  of  the 
intrusive. 

Eastward  along  the  line  of  the  Garlock  Fault,  almost  to  the  border 
of  the  map,  an  occasional  small  exposure  of  basalt  may  be  found.  These 
appear  in  each  case  to  be  small  pipe-like  intrusive  masses  only  a  few 
feet  across  whose  position  has  been  controlled  in  some  way  by  the 
faulting.  Where  these  pipes  cut  beds  of  the  Rosamond  series,  as  for 
example,  two  and  one-half  miles  north  of  Bedrock  Spring,  the'  sands 
and  clays  of  that  series  are  silicified. 

The  name  Black  IMountain  basalt  has  been  adopted  for  this  group 
of  rocks  due  to  the  widespread  basalt  flows  present  on  Black  Mountain, 
seven  miles  west  of  El  Paso  Peaks,  where  they  occur  unconformably 
overlying  Tertiary  sediments.  These  flows  extend  northeastward  almost 
to  the  corner  of  this  quadrangle'.  There  can  be  little  doubt  that  the 
basaltic  intrusives  and  extrusives  of  this  quadrangle  and  the  flows  of 
Black  Mountain  are  correlative.  Basalt  flows,  similar  in  composition 
and  appearance  to  those  here  described,  occur  at  similar  horizons  in 
various  parts  of  the  nearby  desert  province,  as  for  example,  the  flows 
capping  Black  Mountain  (a  different  mountam  from  the  one  above), 
fourteen  miles  east  of  Fremont  Peak. 


—  60  — 

Petrology. 

The  rocks  of  this  group  may  be  classified  as  augite-hornblende  basalts. 
They  are  characteristically  dark  colored,  usually  being  black  but  some- 
times medium  or  dark  gray.  The  groundmass  is  dense  and  stony  in 
appearance  and  is  practically  always  highly  vesicular,  even  in  the 
intrusive  facies.  The  vesicles  possess  extremely  irregular  forms  and 
are  but  seldom  filled.  At  times  a  faint  flow  structure  may  be  made  out. 
Pheuocrysts,  while  usually  present,  are  neither  abundant  nor  conspicu- 
ous. Plagioclase  feldspars  showing  albite  twinning  and  occasional 
prisms  of  hornblende  and  pyroxene  can  be  identified  with  the  hand  lens. 

Microseopioally  the  groundmass  was  found  to  be  composed  of  minute  lath-shaped 
feldspars  and  abundant  scattered  grains  of  magnetite.  The  feldspar  laths  which 
have  the  composition  of  labradorite  always  appear  to  be  arranged  with  their  long 
axes  parallel,  developing  a  flow  structure.  Brown  glass  in  moderate  amounts  was 
sometimes  present. 

The  phenocrysts  were  found  to  consist  of  well-developed  plagioclase  crystals, 
showing  both  albite  twinning  and  zoning.  They  varied  in  composition  from  labra- 
dorite to  bytownite.  Brown  hornblende,  present  in  moderate  amount,  usually  shoiwed 
strong  reaction  zones  of  magnetite.  The  pyroxene  observed  was  identified  as  augite. 
It  was  usually  subordinate  in  quantity  to  the  hornblende.  No  hypersthene  was 
recognized.     In  two  cases  quartz  was  present,  apparently  as  a  primary  mineral. 

Inclusions  which  have  without  doubt  been  derived  from  the  under- 
lying Rosamond  series  are  occasionally  found  in  the  basalts.  The 
writer  observed  fragments  of  both  quartz  and  schists. 

These  rocks  are  very  little  weathered.  At  the  most,  they  show  only 
a  weatherstained  .surface,  so  that  fresh  fragments  are  easily  obtained. 
Due  to  jointing,  the  basalt  breaks  out  in  platey  or  prismatic  blocks 
which  are  strewn  over  the  surface  of  most  of  the  e'xposures. 

Age. 

The  age  of  the  Black  Mountain  basalts  may  be  anything  from  Middle 
Pliocene  to  Pleistocene.  They  are  unconformably  later  than  the  Red 
^lountain  andesites.  as  is  shown  by  the  flow  on  the  side  of  the  ancient 
canyon  on  the  surface  of  the  andesites,  and  by  the  basalt  flows  over- 
lapping on  the  surface  of  the  Rosamond  series. 

The  basalts  on  the  other  hand  are  earlier  than  much  of  the  movement 
along  the  Garlock  Fault.  Boulders  of  basalt  are  incorporated  in 
alluvium  which  has  been  elevated  several  hundred  feet  by  the  faulting. 

The  freshness  of  the  basalts  and  the  persistence  of  portions  of  flows 
which  were  originally  only  a  few  feet  thick,  argue  for  the  recency  of 
their  formation.  tSo  that  it  seems  probable  that  the  Black  Mountain 
basalts  are  very  late  Pliocene  or  early  Pleistocene  in  age. 

ALLUVIUM. 

All  unconsolidated  deposits  of  Quaternary  age  occurring  within 
the  quadrangle  have  been  grouped  together  as  alluvium.  And  only 
those  portions  of  the  alluvium  were  mapped  which  covered  some  con- 
siderable area  aiid  which  were  present  in  sufficient  thickness  to  effec- 
tually mask  the  underlying  formations.  Thus  the  amount  of  alluvium 
mapped  is  necessarily  incomplete  and  approximate  and  materials  of 
different  types  and  different  modes  of  origin  have  been  grouped 
together. 


PLATE   17. 


A.  BLACK  MOUNTAIN  BASALT.  From  intrusive  pipe  near  Summit 
Diggings.  B  =  bytownite  plienocryst ;  groundmass  consists  of  lath 
shaped  feldspars  and  fine  magnetite  crystals  surrounded  by  brown 
glass.     50    dia.     Ordinary   light. 


B.     SAME    AS    -A"     BUT    WITH    XICOLS    CROSSED. 


37841 — facing  p.    GO. 


—  61  — 

Ancient  Gravels. 

The  relative  afre  of  tlie  various  phases  of  the  alluvium  is  usually 
indetermiuate,  hut  in  a  few  cases  at  least  unconsolidated  dejiosits  are 
known  to  antedate  much  of  the  movements  on  the  (iarlock  Fault.  At 
various  points  noi-th  of  the  fault,  as  for  instance  ovei-lyiii<i'  the  Rosa- 
'  mond  ])eds  near  tlie  Hummer  Mine  and  as  a  capping'  on  the  hill  a  mile 
and  a  half  south  of  Laurel  ^Mountain,  alluvium  occurs  which  from  its 
in'csent  position,  must  have  been  elevated  several  hundred  feet  since 
its  oi-i;_Miud  deposition.  Boulders  of  vesicular  basalt,  apparently  dei'ived 
from  Hows  to  the  north  and  west  of  the  ((uadranjile  are  an  im])ortant 
constituent  of  these  deposits.  These  isolated  and  elevated  areas  of 
alluvium  are  remnants  of  an  extensive  ancient  alluvial  deposit  which 
covered  ]iai't  of  the  region  before  important  movements  ocui-red  alons" 
the  Garlock  Fault. 

Other  Alluviums. 

The  valley  between  the  Rand  IMountains  and  the  El  Paso  Mountains 
is  filled  with  a  wedji'e  of  alluvium  which  is  of  great  thickness  near  the 
Garlock  Faidt  and  feathers  out  to  the  south.  Wells  sunk  by  the  Yellow 
Aster  Mining  aiul  Milling  (V)m])any  near  the  fault  line  and  just  west 
of  the  west  border  of  the  map  passed  through  600  feet  of  gravels  before 
i-eaching  bedrock. 

The  materials  present  in  the  alluvium  of  this  valley  all  appear  to  be 
types  dei'ived  from  the  immediate  region.  They  are  fiiu'st  near  the 
center  of  the  vallej',  increasing  in  size  as  one  passes  towards  the 
edge  of  the  alluvium.  All  sizes  of  material  from  silt  to  boulders  several 
feet  in  diametei-  are  represented,  ^lost  of  the  alluvi\im  is  jn-actically 
unassorted,  nncemented  and  usually  nnbedded.  Locally,  however, 
horizons  occur  which  show  some  sorting  while  bedding  and  sometimes 
crossbcdding  are  occasionally  to  be  seen.  In  place's  a  slight  cementa- 
tion by  calcium  carbonate,  locally  called  'caliche,'  has  occurred.  This 
alluvium  has  accumulated  chiefly  through  the  action  of  intermittent 
streams  in  times  of  storms,  an  action  which  is  still  going  on  in  the 
region.  In  the  west-central  part  of  the  valley,  wind-blown  sands  have 
formed  a  .still  more  recent  deposit  covering  the  underlying  and  different 
type  of  alluvium. 

The  alluvium  in  the  region  south  of  the  Rand  Mountains  and  Red 
Mountain  is  quite  similar  to  that  present  in  the'  valley  to  the  north, 
although  in  general  the  materials  are  nuieh  smaller  in  size.  In  the 
western  part  the  alluvium  is  probably  not  of  great  thickness,  but  the 
thickness  probably  increases  towards  the  eastern  border  of  the  map. 

The  quartz  monzonite  in  the  southwestern  part  of  the  quadrangle 
is  quite  free  from  any  cover  of  alluvium,  but  is  covered  with  a  layer 
of  detrital  minerals  derived  from  the'  disintegration  of  the  quartz 
monzonite  in  place.  The  most  abundant  of  these  detrital  minerals  is 
quartz,  so  that  the  surface  of  the  ground  appears  quite  white.  The 
accumulation  of  this  detrital  quartz  in  place  must  represent  the  lapse 
of  a  very  long  period  of  time. 

STRUCTURE. 

The  structures  possessed  by  the  individual  formations  have  already 
been  outlined  in  describing  each  group  of  rocks.     It  only  remains  to 


—  62  ~ 

describe  the  faulting  and  to  consider  such  features  as  will  serve  to 
explain  the  general  regional  structure. 


The  Garlock  Fault. 

The  most  important  structural  feature  of  the  region  is  the  fault 
lino  which  passes  across  the  northern  part  of  the  quadrangle.  This 'I 
fault  is  sliown  on  the  Fault  JNlap  of  California^  as  extending  from 
the  San  Andreas  Rift  near  Gorman,  in  the  northwestern  corner  of  Los 
Angeles  County,  eastward  as  far  as  the  south  end  of  Death  Valley. 
It  is  therefore  one  of  the  most  important  structural  lines  of  California. 

The  mapping  of  the  Garlock  Fault  within  this  quadrangle  shows 
that  it  is  a  rift  feature  with  numerous  branching  subsidiary  faults. 
The  main  fault  is  vertical  or  nearly  so  as  is  indicated  by  tlxe  compara- 
tively straight  course  it  follows  across  the  country.  The  subsidiary 
faults  appear  in  part  at  least,  to  be  the  result  of  small  blocks  slumping 
do^^ai  from  either  wall  of  the  main  fault.  Near  the  west  border  of  the 
map  two  such  blocks  occur  which  have  sunk  below  the  level  of  the  sur- 
rounding country.  One  of  these,  on  the  north  side  of  the  Garlock 
Fault,  is  now  sho■^^^l  by  a  depression  a  mile  in  length,  a  quarter  of  a 
mile'  broad  and  over  fifty  feet  below  the  surrounding  country.  The 
other,  a  half  mile  to  the  west  and  just  off  the  map,  is  roughly  a  quarter 
of  a  mile  in  length  by  an  eighth  of  a  mile  in  width  and  approximately 
seventy-five  feet  deep.  These  depressions  lie  immediately  in  front  of 
the  steep  southern  face  of  the  El  Paso  Mountains  and  are  accumulating 
detritus  from  an  area  of  several  square  miles.  They  therefore  must  be 
the  result  of  very  recent  activity  along  the  Garlock  Fault. 

The  recency  of  the  movement  is  also  indicated  by  the  details  of  the 
topography  along  the  line  of  the'  fault.  The  trimcated  spurs,  the 
tendency  toward  the  development  of  a  subsequent  drainage  and  the 
strong  furrow-like  depressions  locally  present  in  the  alluvium  are 
strikingly  fresh  and  immature. 

The  mapping  of  the  geology  adjacent  to  the  fault  furnishes  some 
evidence  as  to  its  age  and  the  relative  movements  which  have  occurred 
along  it.  The  base  of  the  small  patch  of  Rosamond  beds  on  the' 
summit  of  the  El  Paso  Range  near  tUe  Hummer  Mine  lies  at  an  eleva- 
tion of  about  4000  feet.  The  base  of  the  Rosamond  is  also  exposed  a 
fourth  of  a  mile  south  of  the  fault,  overlying  Paleozoic  sediments  in 
the  northeast  corner  of  Sec.  2,  T.  29  S.,  R.  40  E.,  at  an  elevation  of 
8350  feet.  These  two  exposures  are  approximately  three  miles  apart. 
Apparently  the  north  side  of  the'  fault  has  risen  here  some  650  feet 
relative  to  the  south  side  since  the  base  of  the  Rosamond  series  was 
deposited.  The  steep  escarpment  on  the  south  front  of  the  El  Paso 
Mountains  in  the  western  part  of  the  quadrangle  is  the  direct  result  of 
this  vertical  movement. 

A  suggestion  of  the  horizontal  movement  which  has  occurred  along  the 
Garlock  Fault  is  found  in  the  relative  positions  of  the  contact  between 
the  quartz  monzonite  and  the  Paleozoic  sediments  on  either  side'  of  the 
fault.  North  of  the  fault  the  contact  cuts  directly  across  the  El  Paso 
Mountains  in  a  southeasterly  direction.  Everything  east  of  this  contact 
is  quartz  monzonite,  more  or  less  covered  by  later  deposits.  Across  the 
fault,  however,  we  find  only  Paleozoic  sediments,  very  largely  covered 

•Published  by  the  Seismological  Society  of  America.     1923. 


—  63  — 

by  later  deposits.  These  Paleozoic  rocks  extend  eastward  for  several 
miles  as  shown  by  an  occasional  ontcrop  projectinp-  through  the  more 
recent  deposits.    Their  contact  with  the  quartz  monzonite  soutli  of  the 

PLATE   18. 


A.  LOOKING  EAST  ALONG  THE  GARLOCK  FAULT  LINE.  Taken  from  a 
point  four  miles  from  the  west  edge  of  the  quadrangle  as  measured  along  the 
line  of  the  fault. 


■<m 


srsnrvas:  -•■.  ^ev : 


..-c-r^ 


B.    THE  GARLOCK  FAULT  LINE.      As  seen  looking  east  from  the  bottom  of  the 
'sink  hole'  located  just  west  of  the  edge  of  the  quadrangle. 

fault  is  covered  by  Tertiary  deposits  but  must  occur  somewhere  in  the 
region  a  mile'  and  a  half  to  two  miles  east  of  the  railroad.  Thus,  seg- 
ments of  the  same  contact  on  tlie  two  sides  of  the  fault  are  separated  by 
a  distance  of  roughly  five  miles.    This  distance  appears  to  be  a  measure 


—    64:    — 

of  the  horizontal  displacement  (south  side  to  the  east),  which  has 
occurred  along  the  Garlock  Fault  in  this  region. 

The  time  of  the  inception  of  the  faulting  can  not  be  definitely  deter- 
mined. The  complex  folding  of  the  Paleozoic  rocks  nortli  of  the  Gar- 
lock  Fault  as  contrasted  with  the  apparently  slightly-folded  rocks 
south  of  the  fault  and  with  the  flat-lying  schists  of  Archean  age  is 
suggestive  that  the  Garlock  Fault  may  have  been  a  line  of  weakness 
dating  back  to  the  time  of  the  granitic  invasion. 

The  time  during  which  much  of  the  movement  on  the  Garlock  Fault 
has  occurred  can  be  fixed  ({uite  accurately  however.  All  the  rocks  in 
the  region,  including  the  QuatiCrnary  alluvium  are  involved  in  the 
faulting.  The  occurrence  of  alluvium  containing  boulders  of  Black 
IMountain  basalt  overlying  the  Rosamond  strata  near  the  Hummer 
Mine  has  already  been  described.  The  elevation  of  the  El  Paso  Moun- 
tains above  the  valley  to  the  south  then  must  have  occurred  since  the 
extrusion  of  the  Black  Mountain  Basalt  and  since  the  deposition  of 
this  alluvium.  In  other  words,  the  chief  movements  have  occurred  in 
the  Quaternar}^,  probably  in  the  late  Quaternary,  and  from  evidence 
already  cited,  these  movements  appear  to  be  still  in  progress. 

The  Lava  Mountains. 

The  northward  facing  escarpment  on  the  north  front  of  the  Lava 
jMountains  adjacent  to  and  on  the  south  side  of  the  Garlock  Fault,  as  well 
as  tlie  tendency  of  the  Rosamond  series  in  the  same  region  to  dip  to  the 
south  at  moderate  angles  away  from  the  quartz  monzonite  appear  to 
be  somewhat  anomalous  in  view  of  the  Garlock  Fault  being  downthrown 
on  the  south  side.  The  small  blocks  of  andesite  dropped  down  on  the 
south  side  of  the  fault  in  the  region  three  miles  northeast  of  Summit 
Diggings  show  that  the  south  side  of  the  fault  in  this  part  of  the 
quadrangle  is  truly  the  downthrown  side  however. 

The  explanation  of  this  anomalous  condition  was  found  in  a  flat  fault 
dipping  at  low  angles  to  the  south  and  exposed  for  only  a  short  distance 
in  the  northeast  corner  of  the  quadrangle.  This  fault  appears  to  be  a 
thrust  fault  in  which  the  quartz  monzonite  has  overridden  strata  of 
the  Rosamond  series.  This  fault  is  older  than  the  Garlock  Fault, 
apparently  being  cut  ofl:'  by  that  fault  two  miles  from  the  east  edge  of 
the  (piadrangle.  Movement  on  this  flat  fault  elevated  the  northern 
portion  of  the  Lava  Mountains,  resulting  in  the  stripping  ofi:  of  the 
Rosamond  strata  from  the  quartz  monzonite  in  the  elevated  portion. 
As  has  already  been  seen  in  the  dissection  of  the  Rosamond  series  in  the 
northern  part  of  the  Lava  ^lountains  occurred  before  the  extrusion  of 
the  Red  Miountain  andesites.  Hence  the  age  of  this  flat  fault  would 
be  that  of  late  Rosamond  time  or  late  IMiocene. 

The  wedge-like  point  of  the  block  overlying  this  flat  fault  would  have 
been  shoved  out  into  the  region  north  of  the  Garlock  Fault.  But  since 
it  must  have  consisted  largely  of  Rosamond  strata,  it  could  easily  have 
))een  eroded  away  leaving  the  escarpment  as  Ave  now  find  it.  Upward 
movement  of  the  north  side  of  the  Garlock  Fault  would  merely  tend  to 
reduce  this  escarpment. 

The  Rand  Mountains. 

The  gentle  slope  and  old  surface  south  of  the  crest  of  the  Rand  Moun- 
tains and  the  steep  northern  slope  with  its  youthful  features  is  strongly 


—  65  — 

suggestive  that  the  Rand  Mountains  owe  tlieir  orisfin  to  tilting  and 
faulting.  This  is  borne  out  1)\'  the  presence  of  numerous  steeply 
dipping  faults  along  the  nortiiern  front  of  the  range,  the  strike  of  the 
faults  being  roughly  parallel  to  the  trend  of  the  range.  Locally  these 
faults  are  ([uite  prominent,  but  due  to  the  similarity  of  the  schists 
through  which  they  pass  they  are  dit^cult  to  trace.  Hence  no  attempt 
was  made  to  map  them  in  the  short  time  available  for  this  work. 

These  faults  are  presumably  normal  faults  which  dip  to  the  north- 
west. Of  the  many  wliich  exist,  the  best  known  is  the  Jupiter  Fault 
which  is  extensively  exposed  in  the  workings  of  the  Yellow  Aster  ^Mine. 
Movements  on  this  fault  are  in  part  earlier  than  the  ore  deposition 
which  occurred  in  middle  Upper  ^Miocene  time.  On  the  other  hand 
Rosamond  beds  appear  to  be  involved  in  the  tilting,  which  would  fix 
its  period  as  middle  Upper  Pliocene. 

While  only  normal  faulting  is  known  along  the  north  front  of  the 
Rand  Mountains,  there  is  another  possibility  which  must  not  be  over- 
looked in  considering  the  origin  of  the  range.  That  is  tliat  tilting  and 
elevation  have  been  the  result  of  thrust  faulting.  The  trend  of  the  Rand 
Mountains  is  such  that  if  contiiuied  to  the  northeast  they  would  merge 
with  the  northern  end  of  the  Lava  ^Mountains.  Each  range  possesses  a 
steep  northern  escarpment  overlooking  a  flat  valley.  The  flat  fault  pre- 
sent in  tlie  Lava  ^lountains  is  presumed  to  continue  to  the  west,  cut  off.  by 
the  Garlock  Fault  and  hidden  from  view.  This  fault  might  easily 
swing  to  the  south  beneath  the  cover  of  later  deposits  in  the  vicinity 
of  Summit  Diggings,  and  pass  along  the  south  side  of  the  valley  north 
of  the  Rand  Mountaias.  To  the  southwest  the  Rand  ^Mountain  uplift 
can  be  traced  for  many  miles,  its  northern  escarpment  swinging  to  the 
south,  gradually  decreasing  in  prominence  ancl  diverging  more  and 
more  from  the  line  of  the  Garlock  Fault. 

If  the  uplift  of  the  Rand  ^louutains  is  the  result  of  thrusting,  the 
normal  faulting  observed  along  the  front  of  the  range  and  elsewhere 
in  the  Rand  ^fountains  would  consist  merely  of  subsidiary  l)reaks  in 
the  thin  wedge  overlying  the  tlirust  fault.  This  action  would  involve 
only  compressive  stresses  in  the  region  during  much  of  tlie  Tertiary, 
whereas  if  the  Rand  INIountains  owe  their  origin  to  normal  faulting, 
conditions  of  tension  must  have  existed  as  well  as  the  compressive 
stresses  involved  in  the  flat  fault  of  the  Lava  Mountains. 

Flat  faults  which  are  apparently  minor  thrusts  are  not  unknown  in 
the  Rand  ^lountains.  They  are  commonly  met  with  in  mining  opera- 
tions. The  orebodies  of  the  California  Rand  Silver  Mine  entirely 
underlie  a  flat  fault  which  dips  to  the  east  at  a  low  angle,  while  ore- 
bodies  in  other  mines,  as  in  the  St.  Lawrence  Rand,  have  been  offset 
by  small  flat  faults. 

GEOLOGIC   HISTORY. 

The  firet  event  of  which  the  rocks  of  the  quadrangle  bear  any  record 
was  the  presence  in  Archean  time  of  a  sea  in  which  sediments  were 
being  deposited.  The  abundance  of  limestone  and  fine  clastic  materials 
present  in  these  sediments  testify  to  a  distant  land  ma.ss ;  while  the 
limestones  with  their  content  of  carbonaceous  matter  (now  graphitic) 
suggest  that  life  of  some  form  was  present  in  this  sea.  These  sediments, 
following  their  deposition,  were  subjected  to  intense  pressures  and 
increased  temperatures  which  induced  the  gnessic  features   in   these 

5 — 37841 


—  66  — 

rocks  which  we  now  know  as  the  Johannesburg  gneiss.  Whether  these 
pressures  and  increased  temperatures  resulted  from  deep  burial  of  the 
sediments  or  from  mountain-making  movements  is  not  known. 

There  follows  a  break  in  the  record,  the  next  known  event  being  the 
presence  of  another  .sea  in  later  Archean  time.  The  land  was  probably 
less  far  distant  than  in  the  former  sea,  for  the  sediments  deposited  were 
chiefly  clastic,  though  in  large  part  fine  in  grain.  Volcanic  activity 
was  at  times  intense  in  some  nearby  part  of  the  region,  beds  of  pure 
basic  tuffs  being  deposited.  At  other  times  when  the  volcanic  activity 
was  less  intense  the  tuft's  became  mixed  with  other  sedimentary  material. 
Igneous  intrusions  of  basic  composition  occured  in  connection  with  this 
volcanic  activity. 

Following  their  deposition,  these  sediments  with  the  interbedded 
pyroclastic  material  were  deeph'  biu"ied  beneath  an  immense  load  of 
overlying  rocks.  The  resulting  pressures  and  the  increased  tempera- 
tures due  to  the  depth  of  burial  resulted  in  the  recrystallization  of 
these  sediments  and  pyroclastics  into  schists,  the  Rand  schists  as  we 
now  find  them. 

Whether  the  overlying  load  of  rocks  consisted  entirely  of  Pre-Cam- 
brian  rocks,  or  whether  their  accumulation  oyerlapped  into  the  Paleo- 
zoic is  not  known.  It  seems  probable  however  that  erosion  had  stripped 
oft'  these  overlying  rocks,  exposing  the  schists  before  the  deposition  of 
the  Paleozoic  sediments  of  the  El  Paso  Mountains  had  commenced,  for 
schist  fragments  derived  from  the  erosion  of  metamorphic  rocks  are 
included  in  the  lower  part  of  the  Paleozoic  series.  Hence,  while  most 
of  the  interval  between  the  metamorphism  of  the  Rand  schist  and  the 
beginning  of  the  deposition  of  the  Paleozoic  series  is  a  blank,  it  seems 
Ihat  for  a  part  of  that  interval  at  least  the  region  was  above  sea  level 
and  undergoing  erosion.  The  uplift  of  the  region  above  sea  level  was 
unaccompanied  by  folding. 

Sometime  during  the  Paleozoic  era  the  region  Avas  occupied  by  another 
sea  in  which  was  deposited  a  thick  series  of  marine  sediments.  Though 
during  most  of  this  period  of  accumulation  from  a  distant  land  mass 
resulted  in  the  deposition  of  organic  or  very  ftne  clastic  types  of  rock, 
at  times  fluctuations  of  the  sea  and  land  areas  resulted  in  closer  sources 
of  supply  and  the  deposition  of  coarser  materials.  It  is  not  known 
during  what  portion  of  the  Paleozoic  this  sea  persisted,  nor  whether  one 
or  several  invasions  of  the  sea  occurred. 

Again  the  record  is  interrupted,  not  to  be  resumed  until  the  late 
Jurassic  when  uplift  and  folding  accompanied  by  a  batholithic  invasion 
of  quartz  monzonite  occurred  in  the  region  north  of  the  Garlock  Fault. 
The  region  to  the  south  of  the  fault  suffered  from  the  same  batholithic 
invasion  and  uplift  but  here  tlie  folding  appears  to  have  been  absent. 

No  record  exists  of  any  rocks  liaving  been  formed  in  this  region  from 
the  time  of  the  invasion  of  the  quartz  monzonite  until  the  middle 
INIiocene.  During  this  interval  the  region  appears  to  have  been  a  stable 
land  mass  subject  to  erosion.  It  was  probably  initially  of  high  relief, 
but  by  the  middle  Miocene  its  surface  had  been  reduced  to  the  condition 
of  a  peneplain.  The  quartz  monzonite.  originally  formed  at  depths  of 
several  thousand  feet  below  tlie  surface  was  now  exposed  over  the 
greater  part  of  the  area.  A  good  drainage  system  must  have  existed 
for  the  tremendous  quantities  of  material  which  had  been  eroded  have 
been  entirely  removed  from  the  region. 


—  67  — 

At  the  beginuiug  of  the  Upper  ^Miocene  faulting  and  warping  of  the 
earths  surface  destroyed  this  drainage  system,  causing  the  development 
of  basins  in  which  lakes  were  formed.  Tiiese  lakes  gradually  accumu- 
lated sediments  from  their  immediate  surroundings.  The  climate  at 
this  time  was  arid,  probably  not  vastly  different  from  that  of  the 
present,  so  that  the  sediments  accunudating  showed  but  little  effect  of 
weathering.  The  basins  either  became  tilled  with  sediments  from  time 
to  time,  or  else  the  waters  in  them  evaporated,  so  that  lacustrial  condi- 
tions alternated  with  subaerial. 

The  faulting  and  warping  in  the  Upper  Miocene  appear  to  have  been 
the  result  of  compressive  forces  acting  in  the  region.  They  appear  to 
have  continued  their  activity  throughout  the  time  the  Rosamond  series 
was  being  deposited,  so  that  the  basins  were  being  formed  anew  as  fast 
as  they  became  filled.  And  deposits  already  laid  down  were  uplifted 
and  subjected  to  erosion.  The  nature  of  the  Rosamond  was  such  that 
those  portions  undergoing  uplift  were  probably  eroded  as  fast  as  they 
were  uplifted.  Hence  the  upper  surface  of  the  Rosamond  probably 
tended  to  approach  a  plain  surface  during  mucli  of  its  history,  but 
especially  during  its  late  history. 

The  faulting  and  warping  which  ushered  in  the  Upper  Miocene 
appear  also  to  have  been  the  signal  for  renewed  igneous  activity  in 
the  region,  for  shortly  after  the  lower  beds  of  the  Rosamond  series 
were  deposited  a  series  of  igneous  intrusions  occurred.  The  first 
intrusives  which  appeared  were  of  an  acid  nature,  having  compositions 
varying  from  rhyolites  to  latites.  These  were  followed  after  a  moder- 
ately short  interval  by  intrusions  of  basalt  and  dial)ase.  In  this  region 
these  intrusions  took  the  form  of  dikes  and  pipes  which  barely  reached 
the  surface,  if  that.  But  in  some  parts  of  the  surrounding  region 
similar  igneous  activity  resulted  in  tlows  of  rhyolite  or  basalt.  It  is 
uncertain  whether  the  igneous  activity  was  responsible  for  the  faulting 
and  warping  or  whether  the  reverse  was  true. 

After  much  of  the  Rosamond  series  had  been  deposited  the  com- 
pressive stresses  were  relieved  by  thrusting,  resulting  in  an  uplift  in 
the  region  which  is  now  the  northern  part  of  the  Lava  Mountains. 
Possibly  also  the  Rand  ^Mountains  were  formed  at  this  time  by  the  same 
thrusting  action.  The  Rosamond  strata  were  largely  stripped  from 
the  uplifted  areas,  the  material  removed  being  deposited  elsewhere  in 
tlie  region. 

The  extrusion  of  the  Red  Mountain  andesites  began  in  the  very  late 
Miocene  or  very  early  Pliocene  while  the  dissection  of  the  elevated 
l>ortions  of  the  Rosamond  and  the  deposition  of  Rosamond  strata  in 
the  down-warped  areas  were  still  in  progress.  The  volcanic  activity 
began  with  explosive  violence,  covering  the  surrounding  country  with 
tuffs  and  agglomerates.  The  activity  was  limited  to  the  east-central 
portion  of  the  cjuadrangle.  This  was  followed  shortly  by  flows  of 
molten  lava  which  spread  over  the  comparatively  flat  surface  of  the 
Rosamond  l)eds.  In  the  northern  part  of  what  is  now  the  Lava  Moun- 
tains the  flows  poured  into  the  canyons  which  had  been  formed  in  the 
uplifted  portion  of  the  Rosamond.  In  places  the  canyons  were  filled 
though  elsewhere  the  tongues  of  lava  congealed  while  flowing  down  the 
side  of  a  canyon.  The  lavas  were  derived  largely  from  fissure  flows 
although  it  is  possible  that  some  true  volcanic  vents  existed  in  the 
region. 


—  68  — 

No  i'liitluT  activity  was  manifest  in  the  region  until  late  Pliocene  or 
very  early  Pleistocene  time.  During  this  interval  erosion  was  at  work 
hut  due  to  the  continued  aridity  its  operations  appear  to  have  had  but 
little  importance.  During'  the  late  Pliocene  or  very  early  Pleistocene 
time  igneous  activit}-  was  again  renewed,  this  time  with  the  intrusion 
of  irregular  pipes  of  basalt  in  the  north-central  portion  of  the  quad- 
rangle. Some  of  these  intru.sives  reached  the  surface  and  poured  out 
over  small  surounding  areas  as  thin  flows.  In  other  more  distant  parts 
of  the  desert,  as  at  Black  Mountain,  these  flows  covered  wide  areas. 

Erosion  continued  its  work  following  this,  the  last  igneous  activity 
in  the  region.  The  erosion  was  prol)ably  confined  to  the  more  elevated 
portions  of  the  region  which  at  this  time  (early  Pleistocene)  consisted 
of  the  Rand  ^fountains,  Red  Mountain  and  the  Lava  Mountains.  The 
remaining  and  lower  portions  of  the  region  which  included  what  is  now 
the  El  Paso  Mountains,  gradualy  accumulated  a  coating  of  alluvium. 

Important  movement-^  now  began  along  the  (xarloek  Fault.  The 
movement  was  largely  horizontal,  the  south  side  of  the  fault  moving 
eastward.  But  a  noticeable  vertical  component  was  also  present,  the 
north  side  of  the  fault  moving  upward,  resulting  in  the  development 
of  the  El  Paso  Mountains. 

Erosion  and  movements  ou  the  Garlock  Fault  have  continued  up  to 
the  present,  resulting  in  the  uplift  of  the  El  Paso  iMountains  as  we 
now  see  tliem,  and  in  the  filling  of  much  of  the  lower  portions  of  the 
quadrangle  with  alluvium.  ^Mo.st  of  the  old  alluvium  has  been  stripped 
from  the  uplifted  block  north  of  the  Garlock  Fault. 

The  topography  of  the  Randsburg  quadrangle  as  we  now  see  it  is 
thiLs  a  composite  production.  Portions  of  it,  as  the  El  Paso  ^Mountains 
ai-e  the  result  of  processes  which  are  still  at  work.  The  southern  slope 
of  the  Rand  ^Mountains  is  a  product  of  the  erosion  interval  between 
the  Jurassic  and  the  IMiddle  ^Miocene.  The  upper  surface  of  Red 
iMountain  and  the  Lava  ^lountains  is  the  somewhat  modified  surface  of 
the  lava  flows  as  formed  in  the  early  Pliocene.  And  oft'  the  map  to 
the  northeast  there  exists  slightly  modified  and  titlted  remnants  of 
the  late  ]\Iiocene  surface  of  the  Rosamond  series. 


—  69  — 
PART  II.     MINERAL  DEPOSITS. 


GENERAL   STATEMENT. 

.Vt  least  three  Erroups  of  mineral  deposits  may  be  recognized  within 
the  confines  of  tlie  Randsl)uru'  quadi'angle,  each  bein,!2f  characterized  by 
the  pi'eseiice  of  a  single  valuable  metallic  constituent,  and  each  having 
been  formed  during  a  period  of  mineralization  more  or  less  distinct 
from  the  others.  The  metals  characterizing  these  three  periods  of 
iniiici'jilization  are  in  order  of  age,  (1)  tungsten,  (2)  gold,  and  (3) 
silvci-.  The  arcal  distri))ution  of  these  three  metals  appears  to  be  fairly 
distinct  although  some  overlap  occurs  lietvveen  the  gold  and  tungsten 
and  between  the  gold  and  silver. 

The  principal  i)i'oduction  of  tunusten  has  been  from  fissure  veins 
cutting  tlic  quartz  monzonite  in  the  vicinity  of  Atolia.  Deposition  of 
the  tungsten  ores  occurred  chiefly  through  the  filling  of  open  cavities 
with  little  or  no  replacement  of  the  wall  rocks.  Scheelite  was  practically 
the  oidy  tungsten  mineral  formed,  the  gangue  being  composed  largely 
of  (|uai'tz  and  calcite.  The  scheelite  occurs  in  definite  ore  shoots  of 
triangular  form,  the  apex  of  the  triangle  being  downward.  Post 
mineral  faulting  has  offset  the  veins  at  a  number  of  places. 

Age  and  conditions  of  formation  are  less  well  known  for  the  tungsten 
<leposits  than  for  the  other  t.v})es  of  dei)osits  ])reseut  in  the  (puulrangle, 
but  for  reasons  stated  later  (page  77)  they  are  considered  to  have 
l»een  formed  during  ^liddle  or  early  Upper  Miocene  time  by  deposition 
from  asccndinu'  solutions,  close  to  the  surface,  and  at  low  to  moderate 
temperatures. 

The  gold  ores  occur  either  a.s  fillings  in  imrrow  fi.ssure  veins  or  as 
impregnations  and  stockworks  in  both  the  (juartz  monzonite  and  the 
Hand  schist.  Only  oxidized  ores  have  been  mined,  the  gold  being  in 
The  free  state  and  free  milling.  ]\Iint  returns  indicate  that  the  gold 
is  almost  free  from  any  silver  content.  The  veins  are  usually  not  per- 
sistent. The  gangiie  of  the  veins  consists  of  milky  white  quartz,  some- 
times iron  stained,  which  commoidy  shows  crustification  banding  and 
(Irusy  cavities.  Small  (|UrUitities  of  scheelite  may  at  times  be  present 
indicating  a  close  relationship  to  the  Atolia  tungsten  deposits.  The 
stockworks  consist  of  a  network  of  intersecting  stringers  of  quartz 
which  foi'iu  mineralized  zones  most  characteristically  developed  in  the 
<[uaiiz  monzonite. 

Of  more  special  interast  are  the  impregnations  of  gold  along  frac- 
tures in  schist  or  quartz  monzonite  in  which  gold  and  possibly  small 
quantities  of  sulphides  fpyrite  or  arsenopyrite)  have  been  the  only 
iiiint-rals  deposited,  gangue  minerals  other  than  those  of  the  original 
rock  being  entirely  absent. 

The  gold  deposits  commonly  occur  along  lines  of  pre-mineral  faulting, 
and  are  themselves  frequently  cut  by  later  faults.  These  faults  may 
stand  at  any  attitude,  many  of  them  being  ([uite  flat  and  apparently 
the  result  of  compressive  forces. 

In  certain  of  the  mines,  most  notably  in  the  Yellow  Aster,  the  deposi- 
tion of  the  ore  has  been  directlv  controlled  bv  structural  conditions 


—  70  — 

wliich  have  served  to  hinder  or  entirely  dam  the  upward  migration  of 
the  solutions  carryiner  the  <rold. 

The  gold  deposits  are  known  to  eut  rhyolitie  and  diabasie  intrusives 
of  early  Tapper  Miocene  age.  Hence  the  deposition  of  the  gold  was  at 
least  as  recent  as  the  Upper  ]\Iiocene.  The  deposition  of  the  gold  was  pre- 
sumably the  work  of  ascending  heated  solutions  and  occurred  within  a 
few  hundi'ed  feet  of  the  surface  under  conditions  of  low  pressure  and 
fairly  low  temperatures. 

The  silver  deposits  occur  only  in  definite  veins  in  a  limited  portion 
of  the  area  centering  in  the  California  Rand  Silver  ]\Iine.  The  veins, 
of  which  there  are  two  systems,  one  striking  roughly  north,  the  other 
northeast,  are  deposited  along  definite  lines  of  pre-mineral  faulting. 
The  north-striking  veins  are  the  younger.  The  veins  vary  greatly  in 
size  and  are  fairly  persistent  over  moderate  distances. 

The  silver  minerals  present  in  the  primary  ore  consist  in  order  of 
abundance  of  miargyrite,  stylotypite,  pyrargyrite  and  proustite.  The 
gangue  consists  largely  of  a  very  fine-grained  bluish-gray  quartz  with 
some  calcite,  chalcedony  and  probably  opal.  Angular  inclusions  of  the 
schist  wall  rocks,  crustified  banding  and  drusy  cavities  are  features  of 
the  ore.  While  all  portions  of  the  veins  show  more  or  less  silver 
mineralization,  the  richest  ore  shoots  tend  to  follow  the  lines  of  inter- 
section of  veins  of  the  two  systems. 

Direct  structural  control  over  the  deposition  of  the  silver  deposits 
can  be  demonstrated  in  the  California  Rand  Silver  ^Mine,  gouge  present 
in  a  flat  fault  zone  having  acted  as  an  effectual  barrier  to  the  upward 
movement  of  the  mineralizing  solutions. 

The  silver  deposits  are  known  to  be  later  than  the  diabase  intrusives 
and  are  also  known  to  cut  through  a  gold  vein.  Hence  they  must  have 
been  formed  as  recently  as  the  Upper  ]\rioeene. 

The  deposits  are  presumably  the  work  of  ascending  heated  solutions. 
The  structure  of  the  reuion  is  such  that  the  deposition  must  have 
occurred  at  depths  of  only  a  few  hundred  feet  from  the  surface,  and 
hence  under  conditions  of  low  pressure  and  low  temperature. 

Economically  valuable  placer  deposits  have  been  derived  from  both 
the  tungsten  and  gold  deposits  since  their  formation  during  the 
]Miocene.  While  many  of  these  placer  deposits  are  of  recent  origin, 
others  may  date  back  into  the  Pleistocene  or  possibly  even  into  the  late 
Tertiary. 

No  mineralization  of  economic  importance  is  known  to  have  occurred 
in  the  region  previous  to  ]\Iiocene  time.  The  invasion  of  quartz  monzo- 
nite  during  the  IMesozoie  was  apparently  not  accompanied  by  any 
juetalliferous  mineralization  of  consequence.  In  a  few  places  contact 
zones  show  the  presence  of  traces  of  copper,  but  thorough  pi'ospecting 
has  failed  to  reveal  the  presence  of  workable  deposits. 

TUNGSTEN  DEPOSITS. 

The  deposits  of  tungsten  ore  reach  their  major  development  in  a 
vein  system  which  centers  in  the  vicinity  of  Atolia.  The  veins  here 
occur  cutting  quartz  monzonite.  The  vein  system,  which  strikes 
approximately  X.  80°  E.,  has  a  known  extension  of  over  two  and  a  half 
miles  along  its  strike.     The  mineralization  does  not  appear  to  follow 


—  71  — 

single  continuous  veins,  but  rather  a  series  of  veins  wiiieli  occupy  a 
zone  of  shearing  or  fracturing.  This  zone  is  prol)ably  in  the  neighbor- 
hood of  500  feet  wide  although  a  number  of  parallel  veins  lie  outside 
of  this  limit.  The  veins  present  in  the  zone  of  shearing  are  roughly 
parallel  l)ut  sometimes  unite  or  branch. 

The  veins  dip  at  steep  angles  to  the  north,  the  angle  of  dip  varying 
from  70°  to  76°.  In  some  cases  they  appear  to  merge  in  depth  although 
such  a  mergence  has  not  been  actually  demonstrated.  "While  the  zone 
of  shearing  in  which  the  veins  lie  has  a  general  strike  of  N.  80°  E.,  the 
veins  themselves  have  strikes  varying  from  N.  80°  E.  to  S.  80°  E. 

Tlie  fissures  in  which  the  veins  were  formed  were  fault  fissures. 
AEovcmcut  a]ip(\Trs  to  have  continued  along  these  faults  .subsequent  to 
the  deiiosition  of  tlie  vein  mattei".  for  quite  commonly  the  veins  show 
a  thin  clay-gouge  streak  along  one  or  both  walls.  The  walls  are 
frequently  striated  as  well,  the  striations  commonly  being  nearly 
horizo!ital. 

In  addition  to  later  movements  along  the  planes  of  the  veins,  the 
veins  have  been  cut  by  cross  faults  which  may  cause  offsets  of  from 
ten  to  twenty  feet,  or  where  these  cross  faults  cut  the  veins  at  smaller 
angles  an  overla]>  may  he  developed.  These  later  faults  stand  at  steep 
angles.  In  one  case,  in  the  Papoose  ^Fine,  the  ore  is  said  to  be  cut  off 
at  a  depth  of  190  feet  by  a  nearly  horizontal  fault. 

While  in  the  ma.iority  of  cases  the  cross  faults  which  offset  the  veins 
are  quite  barren  of  scheelite,  showing  the  faults  to  have  been  developed 
latei-  than  the  deposition  of  the  ore,  in  one  or  two  cases  at  least  cross 
faults  which  cut  important  ore  bodies  are  themselves  more  or  less 
mineralized  with  scheelite.  Apparently  faulting  was  in  part  con- 
tempoi-aneous  with  the  mineralization. 

The  horizontal  striations  present  along  the  walls  of  the  veins  in 
certain  places,  as  well  as  the  flat  fault  present  in  the  Papoose  Mine,  are 
suggestive  that  the  faulting,  both  pre-and  post-mineral,  was  the  result 
of  compressive  forces  operative  in  the  region. 

The  veins  are  in  general  narrow.     The  width  of  commercial  ore  is 
in  most  eases  less  than  a  foot,  although  in  some  places  it  may  approach 
five  feet.     Exceptions  are  found  in  the  south  vein  of  the  Union  Mine" 
where  irregular  bunches  of  ore  have  been  mined  which  attained  a  thick- 
ness of  seventeen  feet. 

The  mineralization  within  the  veins  is  quite  erratic.  The  ore  occurs 
in  shoots  or  chimneys  which  are  commonly  roughly  triangular  in  form, 
the  apex  being  downward.  These  ore  shoots  vary  greatly  in  size  and 
thickness,  and  the  tenor  of  the  ore  is  quite  irregular.  The  longest 
shoot  kno^^^l,  that  in  the  north  vein  of  the  Union  Mine,  was  1100  feet 
long  on  the  surface,  gradually  short,ening  with  depth  and  finally  dis- 
appearing at  a  depth  of  700  feet  measured  in  the  plane  of  the  vein  and 
at  a  point  a])proximately  below  the  center  of  the  shoot  on  the  surface. 
In  most  of  the  mines,  how'ever,  the  ore  shoots  were  considerably  shorter 
and  extended  to  depths  of  only  one  or  two  hundred  feet. 

One  of  the  few  ore  shoots  which  has  not  been  bottomed  is  that  in  the 
south  vein  of  the  Union  ]\Iine.  This  vein,  which  was  only  discovered 
in  1916,  was  blind,  extending  upward  only  to  about  200  feet  of  the 
surface.  Both  ends  of  the  ore  shoot  appear  to  be  exposed  on  the  8th 
and  9th  levels  but  not  on  the  10th.     The  vein  has  not  been  prospected 


—  72  — 

below  the  lUth  level.  The  ore  shoot  appears  to  be  roughly  triaii<i'ular 
in  form,  being'  approximately  1100  feet  in  length  on  the  8th  level  and 
only  about  800  feet  in  length  on  the  9th  level.  It  rakes  strongly  to 
the  east. 

The  outline  of  the  ore  shoots  is  very  irregular  in  detail.  They  tend 
to  lens  out  in  all  directions,  either  passing  gradually  into  material  too 
low  grade  to  work,  or  else  disappearing  entirely. 

One  dike  of  diabase  is  known  to  cut  the  deposits,  passing  through  the 
western  Avoi-kings  of  the  Ihiion  Mine.  This  dike  was  not  observed  by 
the  Ma'iter  underground,  but  according  to  Mr.  G.  W.  Beamer,  an 
employee'  of  the  Atolia  Mining  Company,  the  dike  cuts  through  the 
veins.  Fragments  of  the  dike  obtained  from  the  mine  dump  were 
readily  identified  as  diabase,  similar  in  all  respects  to  the  diabase 
obtained  from  other  dikes  in  the  region  which  are  known  to  be  of 
early  Upper  IMiocene  age. 

Scheelite  in  varying  amounts  is  known  to  occur  elsewhere  in  the 
quadrangle  than  in  the  belt  centering  about  Atolia. 

A  short  distance  north  of  Atolia  near  the  contact  between  the  quartz 
monzonite'  and  the  schist,  quartz  stringers  carrying  scheelite  are  known 
to  occur  cutting  both  groups  of  rocks.  Some  of  these  veinlets  are  said 
to  be  associated  with  small  basic  dikes.  Mr.  J.  N.  Nevius  has  described 
such  an  occurrence.^ 

He  says  in  part: 

"  *  *  *  North  of  Atolia,  near  the  siiininit  of  the  low  hills,  are  some  shallow 
shafts  showiim  the  sraiiite  cut  by  very  narrow  dikes  of  a  basic  rock,  and  with  seams 
of  scheelite  from  a  knife  edge  to  2  inches  wide  occurring  irregularly  along  the  sides 
of  the  dike." 

This  occurrence  was  not  seen  by  the  writer.  The  dikes  referred  to, 
however,  are  undoubtedly  diabase  of  Upper  Miocene  age  for  no  other 
small  basic  dikes  are  known  in  this  part  of  the  region.  If  this  be  true, 
these  particular  veinlets  of  scheelite  would  appear  to  be  later  than  the 
intrusion  of  diabase  in  early  Upper  Miocene  time. 

In  the  same  vicinity,  a  thin  veinlet  of  scheelite  has  more  recently 
been  cut  in  sinking  the  shaft  of  the  Kand  Contact  Mine. 

Still  further  north  and  northwest,  in  the  Stringer  District,  scheelite 
has  been  repoi'ted  from  many  veins  worked  for  their  gold  content.  The 
presence  of  scheelite  has  been  recognized  in  gold  ores  from  veins  on 
the  Gold  Bug,  Winne,  Baltic,  Sidney  Peak,  St.  Elmo  and  other  prop- 
erties. Veins  on  the  Jersey  Lily  claim  were  worked  for  their  scheelite 
content  during  the  period  of  tlie  World  War,  while  at  one  time  the 
Yellow  Aster  Mining  and  Milling  Company  installed  a  concentrator  to 
save?  the  scheelite  present  in  the  gold  ores  of  the  Yellow  Aster  Mine. 

MINERALS  OF  THE  DEPOSITS. 

The  mineralogy  of  the  ores  of  the  tungsten  belt  which  centers  about 
Atolia  is  relatively  simple.  Although  some  ten  or  twelve  minerals  have 
been  identified  as  occurring  in  the  deposits,  only  three  are  at  all 
common  while  four  are  extremely  rare. 

QUARTZ.  SiO..  Occurs  in  two  distinct  generations.  The  earlier 
of  the  two  generations  is  a  dense  fine-grained  crystalline  aggregate, 

1  J.  N.  Nevius.  Notes  on  the  Randsburg  Tungsten  District.  Min.  &  Eng.  World, 
Vol.   4.5    (1916).   pp.    7-S. 


—  73  — 

grayisli-whito  in  color,  whose  component  grains  are  too  small  to  be 
resolved  except  under  the  microscope.  This  Hnely  crystalline  (juartz 
Avas  the  first  franfrue  mineral  to  be  deposited  and  composes  an  important 
portion  of  the  ore. 

The  second  p:eneration  of  quartz  is  usually  colorless  and  transparent 
thoufrh  sninetimes  white.  Tt  usually  occurs  in  Avell-formed  hexasronal 
prisms  with  pyramidal  terminations,  which  have  grown  freely  from  the 
walls  of  existin.ir  cavities  or  fractures.  Where  the  growth  of  neighbor- 
ing crystals  has  interfered  with  one  another  a  coarsely  crystalline  gran- 
ular aggregate  may  result. 

SCIIEELITE.  CaWO,.  T^sualiy  pure  white  in  color.  Occurs  in 
the  leaner  ore  in  well-formed  crystals  imbedded  in  fine  grained  quartz. 
Due  to  the  similarity  in  color,  however,  these  eiystals  are  quite  incon- 
spicuous. In  the  higher  grade  ore  the  growth  of  crystals  close  together, 
has  resulted  in  cr.ystalline  aggregates  of  indefinite  form.  The  scheelite 
is  most  easily  recognized  in  the  ore  by  its  well-developed  cleavage. 
(111.)  Cleavage  faces  from  an  eighth  to  a  fourth  of  an  hieh  across  are 
quite  common  ;  exceptionally  one  a  half  an  inch  in  diameter  may  be 
found.  Scheelite  is  the  only  tungsten  mineral  which  has  been  recog- 
nized in  the  ores. 

CALCITE.  CaCO;^.  The  third-ranking  important  mineral  present 
in  the  tungsten  ores.  Ordinarily  the  calcite  is  white  in  color  though 
where  slightly  weathered  it  may  be  stainetl  yellowish  brown,  suggesting 
that  possibly  some  ankerite  or  siderite  may  be  present.  The  calcite 
occurs  both  in  anhedal  grains  and  in  perfectly  developed  crystals.  Both 
simple-unit  rhombohedrons  and  high-order  rhombohedrons  occur.  The 
rliombohedral  cleavage  is  characteristic,  many  of  the  eleavage  faces 
being  over  a  half  inch  across. 

STIBXITE.  SboS.j.  Quite  abundant  in  some  veins;  entirely  absent, 
however,  in  most  eases.  Occurs  in  lead-gray  metallic  crystalline  aggre- 
gates intergrown  with  scheelite  and  quartz.  The  individual  crystals 
present  in  these  aggregates  are  commonly  quite  large  as  is  shown  by 
the  size  of  the  cleavage  faces. 

PYRTTE.  FeSo.  Occurs  in  small  though  varying  quantities  through- 
out the  ore,  though  locally  it  may  be  entirely  absent.  In  much  of  the 
ore  it  is  present  only  in  traces.  Pi'obably  more  abundant  disseminated 
through  the  wall  rocks  than  within  the  veins.  The  pyrite  occurs  as 
well  formed  but  very  minute  crystals  which  commonly  show  the  form 
of  a  cube. 

DOLOMITE.  Ca(Mg,Fe)(CO,),.  Deep  yellow  broAvn  in  color. 
•  Occurs  assoeiated  with  other  carbonates  in  certain  portions  of  the  vein 
I  matter.  The  rhombic  cleavage  and  curved  cleavage  faces  are  charac- 
'  teristie.     Dolomite  is  not  common. 

I 

ANKERITE.    (Ca,Mg,Fe)C03.    ^  %ht  brown  carbonate  possessing 
I  a  perfect  rhombohedral  cleavage  and  occurring  in  association  with  dolo- 
mite,    ^lay  be  siderite  in  part.     Not  common. 

GOLD.  In  the  up])er  i)art  of  the  scheelite  bearing  vein  of  the  Rain- 
stj)rm  Mire  a  gold  pocket  was  found  which  produced  from  $600  to 
$700  in  gold.  This  vein  contains  abundant  stibnite.  No  gold  was  seen 
by  the  writer,  and  aside  from  this  one  pocket  no  other  is  definitely 


—  74  — 

known  to  have  occurred  in  the  tungsten-bearing  veins  of  the  Atolia  belt. 
In  the  Stringer  District,  however,  the  association  of  gold  and  scheelite 
is  fairly  common. 

CHALCOPYRITE.  CnFeS„.  Very  rare  in  the  scheelite  veins  of  the 
Atolia  belt.  Only  a  few  minute  specks  were  identified  microscopically 
by  the  writer. 

CINNABAK.  HgS.  Stringers  of  cinnabar  are  reported  to  have 
occurred  in  the  scheelite-producing  vein  of  the  Union  No.  2  Mine  not 
far  below  the  surface.  Detrital  fragmelits  of  cinnabar  have  also  been 
found  in  the  scheelite  placers  southeast  of  Atolia.  No  cinnabar  was 
observed  by  the  writer. 

PHOSPHORUS  BEARING  MINERAL.  Trouble  has  been  caused 
by  the  phosphorous  content  of  ores  from  the  west  end  of  the  Atolia 
scheelite  belt.  Ores  from  the  east  end  appear  to  be  free  from  phos- 
phorus. The  source  of  the  phosphorus  in  the  ore  has  not  been  identi- 
fied but  is  presumed  to  he  apatite  since  the  phosphorus  content  of  the 
concentrates  can  be  removed  by  treatment  with  acid. 

GRADE   OF  THE  ORES. 

The  tenor  of  the  ore  mined  has  varied  greatly  in  different  parts  of 
the  mines.  Since'  1909  the  average  ore,  taken  bj^  years,  has  varied  from 
S^%  to  nearly  8Wr  of  contained  AVO3.  Locally,  however,  inuch  higher 
grade  ores  have  been  mined.  On  the  seventh  level  of  the  Union  Mine, 
a  portion  of  the  south  vein  which  was  here  5|  feet  in  thickness  was  com- 
posed of  nearly  pure  scheelite.  Over  100  tons  of  high-grade  ore  were 
taken  out  and  sacked  which  averaged  63 9(  of  contained  WO.^.  Pure 
scheelite  contains  80.5%  WO3.  The  ore  now  exposed  in  the  Union 
Mine  is  stated  to  average  between  3^%  and  4%  WO3. 

Scheelite  is  a  mineral  which  is  quite  as  resistant  as  quartz  to  w^eather- 
ing,  and  hence  not  subject  to  secondary  enrichment.  In  consequence 
all  variations  in  the  tenor  of  the  ore  are  primary  and  bear  no  relation 
to  weathering  and  erosion  on  the  present  surface.  This  same  resistance 
to  weathering  has  resulted  in  the  development  of  tungsten  placers  to 
the  southeast  of  Atolia  which  have  been  of  importance  economically. 

ORE  TEXTURES  AND  PARAGENESIS. 

All  of  the  tungsten  ores  and  vein  matter  have  been  deposited  in 
open  fissures  along  lines  of  faulting.  Little  or  no  replacement  of  the 
wall  roeks  has  taken  place.  All  of  the  textures  present  in  the  ore  are 
those  resultant  from  deposition  in  open  cavities. 

The  first  minerals  to  be  formed  consisted  of  scheelite  and  the  early 
generation  of  dense  fine-grained  quartz.  This  quartz  is  practically 
microcrystalline  and  contains  intergrown  with  it  equally  small  grains 
and  crystals  of  scheelite'. 

Scattered  about  the  borders  of  these  areas  of  finely  crystalline  inter- 
growths  there  occur  large  masses  of  scheelite,  sometimes  with  a  good 
development  of  crystal  faces,  at  other  times  in  irregular  grains  or 
aggregates  of  smaller  grains.     These  large  areas  may  include  within 


PT.ATE   19. 


,•^-5 


A.  THIX  SECTION'  OF  SCHEELITE  ORE.  Note  the  automorphic  tend- 
ency of  the  scheelite;  also  the  fine  grains  of  selieelite  scattered 
through  the  quartz.  S  =  scheelite  ;  Q=:very  fined  grained  quartz. 
50   dia.   Ordinary   liKht. 


B.  THIX  SECTION  OF'  SCHEELITE  ORE.  Note  the  brecciation  of 
the  scheelite — a  common  feature.  Also  the  fine  grained  scheelite 
in  the  quartz.  S  :=  scheelite  ;  Q  ^  fine  grained  quartz.  50  dia. 
Ordinary  light. 


37841 — faciiis;  p.  74. 


—  75  — 

their  borders  portions  of  the  fine-prainod  (jiiartz.  Coarsely  crystalline 
aprorre<rates  of  quartz  occur  associated  with  the  larger  masses  of  scheelite, 
either  forming  zones  between  the  scheelite  and  the  finely  crystalline 
quartz,  or  possibly  entirely  surrounding  the  stheelite,  or  at  other  times 
occurring  in  veinlets  cutting  across  areas  of  both  scheelite  and  the 
fine  quartz  aggregates. 

The  size  of  the  individual  grains  of  this  coarse-grained  quartz  varies 
considerably.  While  locally,  a  very  sharp  change  occurs  in  passing  from 
the  coarse  to  the  fine  phases,  in  the  ore  at  large,  no  such  break  exists, 
all  gradations  from  the  finest  to  the  coarsest  being  found.  And  similarly 
over  the  ore  at  large  no  actual  break  exists  between  the  very  fine  grains 
of  scheelite  and  the  coarsest  grains,  all  intermediate  grades  being  found. 

Thus  a  continuous  peviod  of  deposition  of  scheelite  and  quartz  can 
be  made  out,  the  first  portion  of  each  mineral  to  be  deposited  being 
very  fine  in  grain,  and  succeeding  material  gradually  increasing  in 
grain  size  until  w^e  finally  obtain  the  coarsest  material  deposited  last. 
Continuous  movements  also  occurred  along  the  fractures  in  which 
deposition  was  taking  place  for  we  find  the  finer  grained  earliel' 
mineral  aggregates  included  in  and  cut  by  the  later  coarser-grained 
phases. 

The  deposition  of  quartz  outlasted  the  supply  of  scheelite  for  we  find 
the  scheelite  (many  pieces  of  which  are  angular  fragments,  the  result 
of  movements  along  the  walls  of  the  fissure)  cut  by  veinlets  of  the 
coarsely-crystalline  quartz  quite  characteristically. 

The  latest  and  coarsest  quartz  to  form,  which  occurs  lining  the  walls 
of  narrow  fractures  which  cut  all  the  earlier  phases  of  the  ore,  shows 
a  well-developed  comb  structure  or  crustification  which  is  commonly 
symmetrical  with  respect  to  the  walls  of  the  fracture.  In  many  places, 
the  ([uartz  crystals  growing  from  the  walls  of  the  fractures  did  not 
succeed  in  entirely  filling  thein,  but  left  open  drusy  cavities  lined  with 
the  pyramidal  terminations  of  the  quartz  crystals. 

The  calcite  did  not  ])egin  to  crystallize  until  after  most  of  the  quartz 
had  been  deposited,  for  we  find  it  occurring  either  as  a  coarsely  granu- 
lar intergrowth  with  some  of  the  latest  quartz  to  form;  as  a  filling  in 
many  of  the  drusy  cavities  left  after  the  crystallization  of  the  quartz ; 
or  as  a  filling  in  still  later  fractures  which  contain  no  quartz  themselves 
but  cut  other  quartz  veinlets  and  hence  must  have  been  formed  subse- 
quent to  the  deposition  of  the  last  quartz. 

The  oth.er  carbonates,  dolomite  and  ankerite,  where  present  both 
slightly  antedate  the  calcite,  the  calcite  having  been  observed  cutting 
through  them.  The  dolomite  is  slightly  earlier  than  the  ankerite,  being 
occasionally  cut  by  veinlets  of  that  mineral. 

The  pyrite  and  stibnite  appear  to  be  still  older,  both  being  most 
commonly  developed  in  quartz  and  only  rarely  present  in  the  carbon- 
ates. The  pyrite  is  most  commonly  contained  in  the  quartz  (sometimes 
in  the  scheelite),  while  the  stibnite  where  present,  appears  to  be  either 
more  or  less  intergrown  with  the  quartz  or  to  cut  the  quartz  along 
fractures. 

The  following  table  indicates  roughly  the  relative  time  of  formation 
of  the  more  common  minerals  during  the  period  of  mineralization. 


—  76  — 

ORDER    OF    FORMATION. 

(Early)  (Late) 

Quartz  (Fine) (Coarse) 

Scheelite       (Fine^  (Coarse)       ~~ 

Pyrite  

Stibnite  

Dolomite  

Ankerite  

Calcite  

111  addition  to  the  i)urely  text  lira  1  features  of  the  ore  are  the  inclu- 
sions of  Avail  rock  whicli  are  occasionally  found  imbedded  in  the  ore. 
These  fragments  appear  to  be  but  little  if  at  all  replaced  l)ut  may  be 
badly  altered. 

NATURE  OF  THE  SOLUTIONS  WHICH   DEPOSITED  THE  ORES. 

The  material  in  these  veins  was  undoubtedly  deposited  by  ascending 
heated  solutions  which  brought  their  content  of  tungsten  up  from 
great  depths.  As  regards  the  nature  of  these  solutions  but  little  is 
known.  The  solutions  must  have  carried  silica,  lime,  carbonic  acid, 
tungstic  acid,  iron,  antimony,  sulphur,  and  traces  of  mercury,  copper 
and  gold.     Such  an  assemblage  suggests  that  the  solutions  were  alkaline. 

The  progressive  order  of  grain  si/e  of  the  scheelite  and  quartz  com- 
posing the  ore  is  suggestive  of  a  gradual  variation  in  the  composition 
of  the  solutions  depositing  the  ore.  The  initial  material  deposited, 
consisting  of  a  fine-granular  aggregate  of  scheelite  and  quartz  has  been 
tlie  result  of  rapid  deposition  from  numei-ous  centers  of  crystal  propa- 
gation. Such  a  result  might  be  obtained  if  solutions  saturated  at  high 
temperatures  should  approach  the  surface  of  the  earth,  and  through 
having  their  temperature  lowered  should  become  supersaturated  with 
respect  to  silica,  lime,  and  tungstic  acid.  The  low  temperatures 
involved  near  the  surface  of  the  earth  would  also  tend  to  decrease  the 
efficiency  of  diffusion  in  the  solutions  which  would  work  in  favor  of 
small  crystals. 

Should  the  later  solutions  gradually  decrease  in  concentration  the 
rate  of  deposition  would  gradually  become  lessened  with  a  consequent 
increase  in  the  size  of  the  crystals  developed  such  as  is  actually  observed 
in  these  ores. 

POSSIBLE  STRUCTURAL  CONTROL  OF  DEPOSITION. 

Whether  the  solutions  were  circulating  or  whether  the  transfer  of 
material  was  largely  by  diffusion  within  the  solutions  is  not  definitely 
known.  Tlie  writer  has  ol)served  numerous  examples  of  ore  deposition 
where  structural  conditions  have  been  such  as  to  cause  stagnation  of 
the  ore-bearing  solutions  immediately  above  the  place  where  the  ore 
deposition  occurred. 

It  is  suggestive  that  the  south  vein  of  tlie  I^nion  IMine,  the  richest 
selieelit(>  vein  of  the  region,  sliould  be  l)lind,  offering  no  upward  escape 
to  the  mineralizing  solutions,  and  suggesting  their  possible  stagnation. 


PLATE  20. 


A.  SCHEELITE  ORE.  Xote  the  two  generations  of  quartz,  the  quartz 
of  the  latest  generation  filling  a  fracture  in  the  scheelite. 
S  =  scheelite ;  balance  of  section  is  quartz.    50   dia.    X  nlcols. 


•-i»^' 

.4^^;;^^ 


B.    SCHEEEITE  ORE.    Note  the  two  generations  of  quartz.       S  =  schee- 
lite ;  balance  of  section  is  quartz.    50  dia.    X  nicols. 


37841 — facing  p.  76. 


—  77  — 

Other  veins  of  the  region  may  liave  offered  similar  obstaeles  to  the 
upward  miirration  of  solutions,  which  ohstaoles  have  since  been  removed 

liy  erosion. 

AGE   AND   GENESIS   OF  THE    DEPOSITS. 

The  scheelite  deposits  are  believed  to  have  been  formed  in  early 
I'pper  ]\riocene  time  liy  hot  aseendint?  allcaline  solutions  of  mairmatic 
ori^iin,  the  deposition  oecun-inu'  (•U)S('  to  the  surface  under  conditions 
of  relatively  low  pressure  and  low  iciiip('i'atur(\  Sucli  deposits  may 
be  termed  epithermal.^ 

Neither  textures  nor  ininei'als  characteristic  of  liigh  temperature 
or  deep-seated  mineraliz-ation  are  present  in  the  Atolia  ores.  And  yet, 
if  the  scheelite  veins  were  formed  in  connection  with  the  invasion  of 
quartz  monzonite,  they  must  of  necessity  from  their  location  in  the 
fpiartz  monzonite  be  deep  seated  and  his'h  temperature  deposits. 

As  luis  already  been  indicated,  one  of  the  chief  characteristics  of  the 
after  effects  of  the  batholithic  invasion  in  this  region  is  the  strong 
development  of  epidote.  (See  pages  37  and  .S(S.)  Kpidote  is  completely 
absent  from  the  Atolia  veins  as  are  the  orthoclase,  l)iotite  and  muscovite 
characteristic  of  the  hypothermal  veins  further  north  which  have  been 
correlated  with  the  quartz  monzonite  intrusion. 

On  the  contrary,  such  textures  as  are  present  are  those  characteristic 
of  epitliermal  deposits  formed  at  low  temperatures  and  inider  shallow 
conditions.  These  textures  include  open  drusy  cavities,  crustification 
banding,  angular  inclusions  of  the  wall  rocks,  the  fine  grain  of  the 
pyrite  and  the  fine  grain  of  the  (luartz. 

If  not  associated  with  the  quartz  monzonite,  the  next  succeeding 
igneous  activity  known  in  the  region  was  in  early  Upper  ^Miocene  time 
when  the  shallow  rhyolitic  and  diabasic  intrusions  occurred.  The  veins 
are  known  to  be  associated  with  certain  diabase  dikes,  at  least  one  of 
which  cuts  the  scheelite  veins.  And,  as  has  been  already  described 
il)age  72)  another  case  occurs  whei'e  it  seems  pro])al)le  that  the 
scheelite  mineralization  is  later  than  the  diabase.  If  the  scheelite 
mineralization  is  truly  of  Upper  Miocene  age  and  related  to  these 
diabase  intrusives,  the  veins  most  certainly  are  epithermal  for  the 
liresent  surface  at  Atolia  lies  only  a  few  hundred  feet  (if  that)  below 
tlie  surface  existing  in  early  Upper  ^Miocene  time. 

The  most  conclusive  evidence  is  found  in  the  association  of  scheelite 
and  gold  in  the  same  veins,  for  the  gold  deposits  are  definitely  epither- 
mal in  type  and  of  Upper  Miocene  age.  The  presence  of  gold  and  stib- 
nite  in  the  Atolia  veins  has  already  been  described.  At  least  one  gold 
vein  exists  in  the  scheelite  belt,  namely  that  on  the  ]\Turphy  claim. 
This  vein  is  practically  parallel  to  the  scheelite  belt.-  The  similar  atti- 
tude possessed  by  this  vein  and  the  scheelite  veins  is  suggestive  of  a 
close  genetic  relationship.  The  presence  of  stibnite  in  the  scheelite 
veins  is  suggestive  of  a  close  time  relationship  to  the  silver  veins  in 
which  it  is  a  common  mineral. 


»W     Lindgren.      A    Sugfrestion  for    the    Terminology    of   Certain    Mineral    Deposits. 

Econ.   Geol..   Vol.   17    (1921).   pp.  292-294.  ..    ^     ^     „     „   „     .„„ 

^P.  L.  Hess.  Gold  Mining  in  the  Randsburg  Quadrangle.  U.  S.  G.  S.  Bull.  430 
(1909),   p.    45. 


—  78  — 

No  especial  objection  on  general,  grounds  to  postulating  an  epithermal 
origin  for  tungsten  ores  appears  possible.     W.  H.  Emmons  states: 

"Tiinffston  minerals  are  found  in  pegmatite  dikes  and  in  veins  formed  at  all 
depths.'" 

Mr.  Emmons  in  his  textbook  on  Economic  Geology  further  remarks : 

"AlthonKli  the  tungsten  minerals  are  very  common  in  pegmatites  and  in  lodes 
formed  at  considerable  depths,  the  most  valuable  deposits  in  the  United  States  are 
lodes  formed  by  ascending  hot  waters  at  moderate  or  shallow  depths."^ 

POSSIBLE   EXTENSION  OF  THE  TUNGSTEN   DEPOSITS. 

Having  formed  at  shallow  depths  and  low  temperatures  in  close 
approach  to  the  surface,  it  would  appear  probable  that  these  very 
physical  conditions  which  are  referrable  to  the  surface,  have  beeli 
largely  responsible  for  the  deposition  of  the  ore.  Such  being  true,  it 
would  appear  improbable  that  the  deposits  should  continue  downward 
indefinitely  possessive  of  their  present  features. 

Two  possibilities  of  change  exist — namely,  that  the  deposits  in  depth 
might  assume  new  features  and  pass  into  higher  temperature  types, 
or  that  no  deposits  have  formed  except  under  the  direct  control  of  the 
surface.  No  method  exists  for  determining  which  of  these  two  possi- 
bilities is  the  true  one.  In  either  case,  however,  changes  in  the  features 
of  the  deposits  may  be  expected  with  depth,  and  these  changes  may 
well  occur  within  the  limits  of  mining  operations.  Epithermal  deposits 
are  known  to  feather  out,  to  become  slowly  impoverished,  or  through  a 
change  in  mineralogic  and  textural  features  to  assume  new  charac- 
teristics. 

It  is  of  interest  to  note  that  of  eight  ore  shoots  which  have  been 
followed  in  the  Atolia  district,  about  which  information  is  available, 
five  have  feathered  out  at  depths  of  less  than  200  feet;  one'  probably 
feathered  out  at  about  412  feet ;  one  was  faulted  otf  at  190  feet ;  and 
onlv  one,  that  on  the  south  vein  of  the  Union  Mine,  has  not  been 
bottomed.  But  this  last,  which  has  been  opened  to  a  depth  of  about 
598  feet  vertically  below  the  surface,  should  it  continue  to  contract 
in  depth  at  the  same  rate  of  contraction  shown  on  the  levels  above  the 
10th,  will  be  bottomed  at  a  depth  of  approximately  800  feet,  or  300 
feet  below  the  10th  level,  measured  along  the  vein. 

The  chief  possibilities  for  extension  of  the  ore  deposits  in  the  Atolia 
District  are  found  in  the  prol)a])le  existence  of  other  veins  which 
have  not  as  yet  been  discovered.  Epithermal  veins  are  notably  short 
and  erratic. '  Those  here  represented,  possess  but  poor  outcrops.  It 
seems  highly  improbable  that  all  of  the  scheelite-bearing  veins  have 
been  discovered.  The  best  possibilities  are  for  other  veins  paralleling 
those  noAv  known  and  roughly  in  the  same  zone,  and  for  possible 
extensions  along  the  strike  of  the  knoAvn  zone.  Further,  the  possibili- 
ties of  other  blind  vems,  such  as  the  south  vein  of  the  Union  Mine 
must  not  be  overlooked.  Such  veins  would  only  be  discoverable 
through  underground  crosscut  ting. 


»^V.  H.  Emmons.     The  Enrichment  of  Ore  Deposits.     U.   S.  G.   S.  Bull.   625,  p.  428. 
»W.  H.  Emmons.     The  Principles  of  Economic  Geology,  p.  525.      (1918.) 


—  79  — 
GOLD  DEPOSITS. 

FIELD  RELATIONS. 

The  p-old  mineralization  is  more  \vi(lesi)n>a(l  than  tliat  of  any  of  the 
other  types  present  in  the  Ran(lsbnr<,'  qnadrantih-.  The  deposits  from 
whii'li  the  eliief  prodnetion  has  eome,  are  h)eated  for  the  most  part, 
witliin  a  radius  of  about  a  mik^  from  Kandsburg,  or  in  the  Stringer 
]~)istriet  on  the  south  side  of  the  Rand  Mountains  south  of  Kandsburg. 
lint  all  the  gold  is  not  confined  to  these  two  areas  by  any  means.  Some 
production  has  been  obtaiiunl  from  the  St.  Elmo  properties  located  in 
the  (juartz  monzonite  south  of  Atolia,  and  numerous  gold  prospects  are 
found  throughout  the  Rami  Mountains.  Some  of  these  have  at  times 
had  a  minor  production. 

In  the  northern  part  of  the  quadi-angle,  a  inimber  of  prospects  are 
found  in  the  vicinity  of  Laurel  Mountain,  the  El  Paso  Peaks  and  west- 
ward through  the  El  Paso  ]\[ountains.  One  or  two  of  these  have  at  differ- 
ent times  made  shipments  of  small  quantities  of  ore. 

The  gold  deposits  of  the  Rand  ^Mountains,  including  such  outlying 
deposits  as  those  at  St.  Elmo,  present  many  similarities  among  them- 
selves and  undoubtedly  have  all  been  formed  during  a  single  period  of 
minei'alization.  What  variation  does  exist  is  chietly  the  result  of  the 
effects  of  local  structure,  accompanied  by  such  erratic  features  of 
mineralization  as  might  be  expected  in  any  similar  group  of  deposits. 
Tims,  while  many  deposits  might  be  classed  differently  on  the  basis  of 
form,  or  size,  or  structure,  the  numy  similarities  of  the  deposits  nullify 
any  such  distinction. 

The  deposits  are  almost  entirely  confined  to  areas  of  quartz  mon- 
zonite or  of  the  Rand  schist.  But  this  association  is  only  the  result 
of  chance  and  does  not  indicate  any  control  of  dei)osition  by  these  joar- 
Ticular  rocks.  Deposition  would  have  proceeded  in  a  similar  manner 
had  other  rocks  than  schist  or  quartz  monzonite  been  present. 

Besides  occurring  in  schist  and  (|uartz  monzonite,  the  gold  deposits 
quite  characteristically  occur  cutting  dikes  of  both  the  rhyolite-latite 
series  and  of  the  diabase-basalt  series.  Such  intersections,  in  Avhich  the 
gold  veins  are  distinctly  younger  than  the  dikes,  are  quite  common. 
But  in  no  instance  has  the  reverse  case  of  a  dike',  either  acid  or  basic, 
cutting  a  gold  deposit  been  observed. 

Besides  the  mere  observation  that  the  gold  deposits  commonly  occur, 
intersecting  dikes  of  the  two  series  mentioned,  there  also  exists  a 
noticeable  similarity  in  the  areal  distribution  of  the  dikes  and  of  the' 
gold  deposits.  This  common  areal  distribution  is  so  striking  that  there 
can  be  little  question  but  that  a  direct  relation  exists  between  the 
dikes  and  the  deposition  of  the  gold.  This  relation  holds  not  only 
within  the  Rand  Mountains  but  also  in  the  vicinity  of  Laurel  Mountain 
and  the  El  Paso  Peaks  where  dikes  of  hornblende-hypersthene  micro- 
diabase  occur.  Outside'  the  quadrangle  at  Fremont  Peak,  rhyolitic  and 
diabasic  dikes  occur  associated  with  the  gold-silver  deposits.  At  the' 
Silver  Dome  Mine,  still  further  south,  rhyolitic  and  diabasic  dikes 
again  occur,  the  vein  along  which  the  mine  workings  have  been 
opened  being  deposited  along  a  brecciated  diabase  dike.    Both  of  these 


—  80  — 

last-named  deposits  are  in  the  quart/  nionzonite,  althongh  the  Silver 
Dome  Mine  is  quite  close  to  an  intrusive  contact  between  the  quartz 
mouzonite  and  marine  Paleozoic  sediments. 

Deposition  of  the  gold  ores  has  commonly  followed  the  lines  of 
intrusion  of  the  dikes,  so  that  the  dikes,  either  rhyolitie  or  diabasic, 
may  occur  as  walls,  either  hanji:ing  or  foot,  to  the  gold  deposits.  Or 
the  gold  vein  may  follow  first  one  wall  of  the  dike,  and  then  intersect 
tlie  dike  and  follow  the  other  wall. 

In  the  Yellow  Aster  Mine  the  ore  may  be  observed  cutting  across 
rhyolite  dikes  at  a  number  of  places.  No  diabase  was  seen  in  this 
mine,  though  it  outcrops  in  several  places  on  the  surface  of  the  prop- 
erty. The  Butte,  Kenyon,  Wedge  and  Little  Butte  are  located  along 
a  single  large  diabase  dike.  The  ore  is  said  to  follow  either  wall  of 
the  dike,  cutting  across  it  in  places. 

In  the  King  Solomon  Mine  the  ore  was  observed  cutting  through  a 
large  diabase  dike.  In  part,  it  roughly  follows  the  trend  of  the  dike. 
In  the  Operator  Divide  Mine  the  ore  was  observed  cutting  through 
dikes  of  both  series,  and  in  one  part  of  the  mine  a  narrow-  diabase  dike 
was  noted  forming  the  hanging  wall  of  the  vein. 

Other  properties  in  which  gold  ores  were  observed  cutting  dikes  of 
either  or  both  series,  include  the  Minnehaha  and  Big  Gold.  At  Fremont 
Peak  one  of  the  veins  which  has  been  explored,  has  through  part  of  its 
course,  dikes  for  both  hanging  and  foot  walls. 

STRUCTURE  OF  THE  DEPOSITS. 

Structurally,  the  gold  deposits  might  be  subdivided  into  several 
groups,  but  such  a  subdivision  would  have  but  little  meaning  and 
would  be  quite  misleading.  All  of  the  ore'  deposition  has  taken  place 
along  fractures  in  the  rock  mass.  Many  of  these  fractures  are  simple. 
Others  are  complex  fracture  systems.  In  some  of  the  fractures  no 
evidence  is  at  hand  to  indicate  any  relative  displacement  of  the  two 
walls.  In  others,  a  displacement  has  occurred,  in  some  cases  large, 
in  other  cases  trivial,  so  that  these  fractures  must  be  recognized  as 
faults.  And  as  might  be  expected  from  the  preceding  discussion,  the 
persistence  of  these  fractures,  whether  faults  or  otherwise,  is  quite 
variable,  though  their  extent,  or  at  least  the  extent  of  that  portion 
which  is  mineralized  is  usually  rather  small. 

The  fractures  along  which  gold  ores  have  been  deposited,  show  a 
wide  variation  in  strike  and  dip.  This,  in  conjunction  with  their 
lack  of  persistence,  makes  any  generalization  regarding  their  attitudes 
somewhat  ditheult  and  uncertain.  Two  general  systems,  however,  can 
be  recognized  into  which  many  of  the  veins  would  fit.  The  strongest 
system  possesses  a  mean  strike  approximately  N.  80°  E.,  or  roughly 
parallel  to  the  Atolia  scheelite  belt.  The  second  strongest  direction  of 
vein  development  is  approximately  northwest  and  southeast.  Many 
exceptions  are  known  Avhich  would  not  fit  well  into  either  of  these 
two  sj'stems. 

The  trend  of  the  Atolia  sehe'elite  belt  Avould  suggest  that  those 
fractures  possessing  a  trend  of  N.  80°  E.,  or  thereabouts,  in  which 
gold  veins  have  been  deposited,  may  be  slightly  older  than  the  frac- 
tures possessing  the  northwest  trend.  It  seems  probable,  however, 
that   both   fracture   systems   were   developed    at    the    time   the    gold 


—  81  — 

mineralization  occurred  for  there  is  no  known  evidence  of  differing 
ago  among  the  gold  veins  themselves. 

The  fractures  in  Avhich  the  ,uold  was  deposited,  vary  greatly  in  angle 
of  dip.  In  many  cases,  as  in  the  Sunshine  Mine  and  the  NW-SE 
veins  of  the  Yellow  Astei-  Mine,  the  veins  stand  vertical.  Tn  other 
mini's  almost  any  intervening  di])  may  be  ob.servrd  down  to  the  angle 
of  20°  to  22°  obsen'ed  in  the  vein  being  worked  by  the  Operator 
Divide  Mine. 

As  has  already  been  implied,  the  walls  of  many  of  the  veins,  both  the 
.steeply-dipping  ones  and  llioso  possessing  a  tial  dip,  commonly  show 
evidence  of  strong  movements.  Where  definite  evidence  of  displace- 
ment of  the  walls  exists,  sharply-defined  vein  walls  usually  result. 

In  certain  cases,  both  walls  of  the  v(^in  may  be  well  defined.  Gouge 
may  or  may  not  be  present  as  a  selvage  bordering  the  vein,  while  the 
walls  may  be  polished  and  striated.  In  such  a  case  the  ore  is  con- 
fined to  a  definite  vein  whose  limits  are  (juite  sharp.  Deposits  where 
the  veins  possess  this  feature  of  two  sharp  walls  are  found  in  the 
Black  Hawk.  Sunshine  and  Sidney  Peak  mines.  It  is  in  such  veins 
where  both  walls  are  quite  definite  and  sharp  that  the  maximum 
amount  of  gangue  minerals  has  been  deposited,  ap])arently  as  a 
filling  in  an  open  fault  fissure.  Such  veins  swell  and  pinch  from 
|)lace  to  place.  They  are  usually  narrow,  probably  averaging  less 
than  a  foot  in  thickness,  though  locally  they  may  lens  out  to  six  or 
seven   feet. 

]\Iany  of  the  veins,  especially  those  with  low  or  moderate  dips, 
l)os.sess  oidy  a  single  definite  wall,  usually  only  a  hanging  wall,  though 
ill  some  cases  a  suggestion  of  a  footwall  may  be  present.  This  well- 
defined  wall  is  commonly  a  definite  line  of  movement  possessing  a 
clay  gouge  and  being  polished  and  striated.  Such  veins  may  show 
but  little  development  of  gangue  minerals  other  than  as  local  lenses 
immediately  underlying  the  fault.  In  other  cases  vein  matter  may 
be  more  prominent.  Frequently  the  ore  consists  of  a  layer  of  the 
country  rock  underlying  the  line  of  faulting,  the  rock  having  been 
impregnated  by  gold  and  to  some  extent  by  quartz  and  other  minerals. 
The  ore  grades  off  into  the  uninineralized  country  rock,  the  two  not 
being  separable  by  the  eye.  The  thickness  of  such  mineralized  zones 
underlying  dipping  faults  varies  from  only  a  few  inches  in  some 
deposits  to  as  much  as  sixteen  feet  in  certain  portions  of  the  Yellow 
Aster  ]\Iine.  Examples  of  orebodies  characterized  by  mineralized 
country  rock  underlying  a  well-developed  hanging  wall  formed  by 
faulting,  are  found  in  the  ore  bodies  underlying  the  .Iu])iter  Fault 
in  the  Yellow  Aster  Mine,  and  in  the  veins  being  worked  in  the 
Operator  Divide  Mine.  A  slight  modification  is  found  in  the  veins  of 
the  King  Solomon  Mine,  both  walls  being  fairly  well  defined,  the  zone 
between  being  filled  with  brecciated  country  rock  which  has  been 
mineralized. 

Still  another  series  of  orebodies  are  to  be  found  which  possess  no 
well-defined  walls,  but  consist  merely  of  mineralized  zones  of  country 
rock  bordering  fractures.  Such  zones  may  be  vertical  or  inclined. 
They  are  probably  best  exemplified  by  the  series  of  vertical  ore- 
bodies  formerly  present  in  the  Yellow  Aster  Mine,  such  as  the  East 
Sets,  the  West  Sets,  and  the  Rand  Vertical  vein.     The  openings  along 

fi— 37841 


—  82  — 

M'hich  tlie  solutions  ascended,  appear  to  have  been  fractures  rather 
than  faults,  hence  the  absence  of  definite  walls.  The  solutions  per- 
meated the  walls  adjacent  to  the  trunk  fractures  depositing  their 
burden  of  gold  and  gangue  minerals.  The  gangue  minerals  other 
than  those  of  the  original  rock  are  not  abundant  in  mineralized  zones 
of  this  class,  at  the  most,  there  being  developed  only  a  network  of 
narrow  quartz  veinlets  cutting  the  rock  mass.  The  mineralization  of 
the  country  rock  along  such  fractures  may  be  only  a  few  inches  thick, 
or,  as  in  the  case  of  the'  East  Sets  of  the  Yellow  Aster  Mine,  the  zone 
may  be  as  much  as  75  feet  in  thickness. 

The  distinctions  which  have  been  drawn  in  the  preceding  discussion, 
have  been  made  solely  with  the  intention  of  emphasizing  the  features 
of  the  original  fracture  in  which  the  deposition  occurred,  and  the 
control  possessed  by  the  fracture  on  the  features  of  the  resulting 
orebody.  Where  an  open  fault  with  definite  walls  occurred,  a  definite 
vein  filling  resulted.  Where  no  large  openings  existed  adjacent  to  the 
fault,  the  deposition  took  place  in  the  rock  mass  underlying  the  fault, 
the  resulting  orebody  possessing  only  a  single  sharp  wall.  And  where 
the  solutions  entered  along  zones  of  fracturing  which  possessed  no 
sharp  walls,  the  country  rocks  adjacent  to  the'  fractures  became 
mineralized  without  definite  walls  to  the  resulting  orebody. 

The  lack  of  persistence  of  many  of  the  veins  has  already  been  men- 
tioned. The  veins  may  terminate  under  varying  conditions.  They 
may  feather  out  in  any  direction  through  complete  disappearance  of 
Ihe  vein  matter,  or  where  vein  matter  is  insignificant  in  amount,  through 
disappearance  of  the  gold  values.  They  may  fork  into  several  branches 
which  mav  in  turn  feather  out.  Or  thev  mav  be  faulted  off.  In  addi- 
tion,  the  original  fracture  in  which  the  deposition  occurred,  may  have 
been  short  and  discontinuous,  either  feathering  out  itself  or  terminat- 
ing at  an  intersection  with  another  fracture,  so  that  the  resulting 
vein  which  was  deposited  was  controlled  by  the  limits  of  the  original 
fracture.  It  is  not  alwa.ys  an  easy  matter  to  decide  in  just  what  manner 
a  vein  is  terminated.  In  many  cases  it  appears  probable  that  veins 
which  are  generally  believed  to  have  been  faulted  off,  really  terminate 
against  what  were  pre-mineral  faults  which  formed  the  original  limit 
of  ore  deposition.  This  appears  to  be  true  for  the  northwest-striking 
veins  of  the  Yellow  Aster  Mine  which  include  the  combined  East  and 
West  Sets,  the  Rand  Vertical  and  the  Price  veins,  all  of  which  are 
terminated  by  the  Jupiter  Fault,  a  fault  of  both  pre-mineral  and  post- 
mineral  movements. 

The  actual  length  of  known  orebodies  which  have  been  worked, 
varies  through  wide'  limits.  xVmong  the  longer  ones  are  the  three 
veins  of  the  Yellow  Aster  ]\Iine  mentioned  in  the  last  paragraph 
which  have  lengths  of  approximately  800,  .500  and  500  feet  respect- 
tively.  The  vein  worked  in  the  Sunshine  Mine  is  said  to  have  been 
about  500  feet  in  length.  With  these  as  upward  limits,  all  lengths  of 
veins  are  known  down  to  the  small  segment  of  a  vein  recently  found 
in  the  Monarch  Rand  workings  which  was  cut  off  on  the  top,  bottom 
and  both  ends  by  faults. 

The  great  majority  of  the  gold  deposits,  (possibly  all)  have  been 
effected  by  complex  post-mineral  faulting  which  may  offset  the  veins 
through  short  distances,  or  as  has  already  been  stated,  may  completely 
terminate  the  known  portion  of  the  deposit.     These  post-mineral  faults 


—  83  — 

have  in  many  properties  been  elassed  as  normal  fanlts,  and  in  many 
cases  they  appear  to  lie  sneli.  Suffice  it  to  say  that  tliese  fanlts  show 
variations  in  dip  from  vertical  to  horizontal  so  that  it  seems  probable 
that  they  have  resulted  in  part  at  least  from  compressive  forces. 

NATURE  OF  THE  VEINS. 

The  major  portion  of  the  prold  ores  which  have  been  mined  in  this 
region  have  been  oxidized.  In  view  of  this  fact  considerable  trouble 
was  encountered  in  obtaining  specimens  in  wliich  the  nature  of  the 
original  primary  mineralization  could  be  studied.  F'urther  difficulty 
was  encountered  in  attempting  to  study  the  metallic  minerals  by  means 
of  the  reflecting  microscope  due  to  their  sparse  distribution  in  the  ores. 
The  material  studied  consisted  of  fragmentary  specimens  obtained  in 
part  underground  and.  in  part  from  dumps  of  mines  not  now  being 
worked.  The  results  will  serve  to  bring  out  the  more  important  phases 
of  the  primary  mineralization  but  may  be  somewhat  incomplete  as 
regards  certain  of  the  details. 

Mineralogy. 

The  mineralogy  of  the  gold  deposits  appears  to  be  fairly  simple,  so 
far  only  11  minerals  having  been  identified  which  are  definitely  associ- 
ated with  the  gold  deposits  of  the  Randsburg  and  Stringer  Districts. 

QUARTZ :  Ordinarily  white  in  color,  sometimes  with  a  faint  bluish 
tinge,  or  in  the  oxidized  ores  faintly  yellow.  Where  present  in  well 
formed  crystals,  not  an  uncommon  feature,  it  is  sometimes  clear  and 
transparent.  Quartz  is  the  only  abundant  vein-forming  mineral  present 
in  the  gold  deposits. 

ARSENOPYRITE :  The  most  abundant  sulphide  present  in  the  pri- 
mary gold  ores.  Arsenopyrite  is  a  brilliant  silvery-white  metallic 
mineral  which  tends  to  assume  a  well-developed  crystal  form.  It  can 
usually  l)e  identified  by  its  triangular  crystal  faces  which  are  quite 
commonly  heavily  striated  due  to  twinning.  In  a  number  or  fragments 
of  ore  picked  up  on  the  dump  of  the  Sunshine  ]\Iine  a  few  fairly  large 
cry.stals  of  arsenopyrite  were  present  whose  crystal  faces  showed  a  pro- 
nounced curvature — an  uncommon  feature  apparently  the  result  of 
strain.  ^Most  of  the  arsenopj^rite  crystals  present  in  the  gold  ores  are 
quite  small. 

PYRITE :  Noticeably  subordinate  in  quantity  to  the  arsenopyrite. 
Occurs  in  very  minute  brass-colored  crystals  of  cubic  or  modified  cubic 
form.  Occasionally  a  crystal  as  much  as  gV  of  an  inch  across  is  observed 
although  crystals  as  large  as  that  are  rare.  While  usually  present  in 
some  quantity  in  all  unoxidized  vein  matter,  pyrite  is  apparently  most 
abundant  in  the  wall  rocks  immediately  adjacent  to  the  veins. 

GALENA:  Not  commonly  observed  being  present  only  in  .small 
amount  and  occurring  in  very  minute  crA'stalline  masses.  Where 
present  in  masses  large  enough  to  be  identified,  the  surface  is  usually 
seen  to  be  blackened  as  the  result  of  alteration.  Though  present  only 
in  small  quantity,  galena  appeal's  to  play  an  important  role  in  the  gold 
mineralization. 

GOLD :  Quantitatively  present  only  in  very  small  amount.  The 
specimens  observed  bv  the  writer  were  quite  irregular  in  form  and 


—  84  — 

appeared  to  vary  somowhat  in  color,  from  light  to  darker  yellow,  sug- 
gesting a  variable  composition.  The  gold-silver  ratio  is  known  to  vary 
consideral)ly  in  different  mines. 

SCHEELITE:  Present  in  small  to  moderate  quantities  in  many  of 
the  gold  veins  of  the  district,  most  notably  in  veins  on  the  Jersey  Lilly, 
Gold  Bug.  Winnie,  Baltic,  St.  Elmo,  Yellow  Aster,  Sunshine,  Consoli- , 
dated  and  Cock  Robin  properties.    Its  presence  is  usually  determinate 
by  panning  a  sample^  of  the  ore.     No  specimens  were  obtained  in  which  I 
the  relation  of  the  scheelitc  to  tlic  gold  could  be  determined. 

TALC  :  A  soft  faint  green  mineral,  apparently  talc,  is  occasionally 
observed  intergrown  with  (|uartz  vein  matter  in  very  small  Hakes. 
Quite  subordinate  in  imjxji-tance. 

IRON  OXIDES :  Very  al)undant  as  porous  masses  or  coatings  along 
fractures  in  the  oxidized  portions  of  the  deposits.  Probably  derived 
from  the  oxidation  of  pyrite  and  arsenopyrite.  The  oxides  are  of 
various  shades  of  yellow-browu  and  are  prol)ab]y  hydrous. 

CALCITE :  Occurs  as  crystalline  coatings  lining  the  walls  of 
fractures  cutting  the  gold  dejxjsits.  The  individual  crystals  are  com- 
monly of  fair  size  and  possess  good  crystal  forms,  that  most  frequently 
observed  being  high-order  rhombohedrons.  The  calcite  is  distinctly 
later  than  the  gold  veins  and  not  necessarily  deposited  by  the  same 
solutions. 

OTHER  .MINERALS:  In  addition  to  the  minerals  listed  above,  F.  L. 
Hess^  mentions  having  observed  chalcopyrite  and  sphalerite  in  the  ores 
of  the  Snnshine  ]\Iine.  These  two  minerals  were  not  observed  by  the 
writer  in  the  gold  ores  of  this  region,  but  at  Fremont  Peak  and  at  the 
Silver  Dome  Mine  copper  minerals  are  fairly  abundant,  especially  so, 
at  the  latter  mine.  Mr.  Hess  also  states  that  analyses  show  the  presence 
of  small  (piantities  of  tellurium  in  the  ores  of  the  Sunshine  ^line. 
Analyses  of  samples  from  the  Hig  Gold  i\Iine  also  show  the  presence 
of  small  quantities  of  tellurium  according  to  ^Ir.  Pearce,  the  engineer 
in  charge.  So  far,  however,  the  mineral  from  which  the  tellurium  has 
been  derived  has  not  been   idciitiHcd. 


ORE  TEXTURES  AND  PARAGENESIS. 

For  purposes  of  description  the  gold  veins  will  be  divided  into  two 
groups,  the  first  in  which  the  ore  consists  of  a  definite  vein  filling  and 
the  second  in  which  the  ore  is  mineralized  country  rock.  All  interven- 
ing stages  may  be  recognized  in  the  field. 

Where  the  ore  consists  of  a  definite  vein  filling,  quartz  is  by  far  the 
most  important  mineral.  Where  the  veins  are  thick  the  textures  of  the 
ore  are  (piite  comparable  to  those  observed  in  the  Atolia  tungsten-bear- 
ing veins.  The  (piartz  varies  in  size  of  grain  from  very  fine  to  moder- 
ately coarse,  the  finer  grained  material  being  definitely  the  earlier  phase 
to  form,  successive  generations  of  quartz  being  coarser  and  coarser.  The 
boundaries  of  the  coarse  grains  are  quite  connnonly  irregular,  the 
irregularity  l)eing  controlled  and  produced  by  the  outlines  of  the  numer- 
ous adjacent  finer  grains. 

'F.  L.  Hess.     U.  S.  G.  S.  Bull.   430,  p.   42. 


U 


—  85  — 

The  finer  grained  (|iiai'tz  oceiirs  as  a  gfaiiular  mosaic,  the  adjaeent 
fjrains  possessintr  comnion  houiularies  which  have  resulted  from  inter- 
ference of  the  growing  crystals.  The  coarser  quartz  grains  may  form 
simihir  mosaics  Avith  conunon  boundaries  among  themselves,  but 
xt'iKimorjihic  towards  the  finer-grained  matei'ial,  or  they  nuiy  occur 
filling-  fractures  cutting  the  earlier  tine-grained  (|uartz.  The  ({uartz 
filling  of  such  fractures  commonly  shows  a  comb  structure,  the  indi- 
vidual crystals  having  gi-own  from  the  walls  of  the  fracture.  Very  com- 
inoidy  these  fractui-es  have  not  been  completely  healed  so  that  open 
druses  occur  which  are  linctl  with  small  pro.jecting  (juartz  crystals. 

An  occasional  small  flake  of  talc  occurs  api)areutly  intergrown  with 
the  quartz,  the  exact  stage  of  its  format ii»n  being  somewliat  indeter- 
minate, however. 

Small  includetl  fragments  of  the  wall  rocks  are  freiiuently  met  with  in 
the  vein  matter.  These  fragments  are  almost  always  badly  altered,  in 
many  cases  being  almost  beyond  recognition. 

Where  the  openings  in  which  the  vehis  were  deposited  were  narrow 
the  complete  filling  may  have  resulted  through  the  growth  of  quartz 
crystals  from  the  walls  of  the  original  fissure.  In  such  cases  the  veins 
show  a  strongly  developed  comb  structure  and  usually  numerous  and 
(|uite  commonly  large  drusy  cavities. 

The  deposition  of  the  metallic  minerals  ai)parently  did  not  l^egin 
until  much  of  the  quartz  gangue  had  been  deposited  for  we  find  them 
best  developed  towards  the  central  part  of  the  comb  structure  of  sucli 
veins.  In  other  cases  the  metallic  minerals  are  observed  deposited  in 
the  gouge  material  of  the  vein  walls,  apparently  later  than  the  vein 
filling. 

Arsenopyrite  and  pyi-jte  were  the  first  of  the  metallic  minerals  to  be 
deposited,  whether  simultaneously  or  otherwise  not  being  determinate. 
Deposition  of  these  sulphides  occurred  directly,  in  part  at  least,  for  we 
find  them  deposited  between  quartz  crystals,  the  deposition  having  taken 
place  appai-ently  while  the  quartz  crystals  were  still  in  process  of 
growth.  Locally,  however,  some  quartz  may  have  been  i-eplaced  for 
there  is  a  noticeabh'  tendency  for  the  pyrite  and  arsenopyrite  to  assume 
a  well-developed  crystal  form.  Some  of  the  arsenopyrite  crystals  are 
bent  and  fractured,  the  fractures  being  filled  with  quartz.  Apparently 
stresses  were  active  while  the  ore  was  being  d(>posit(>d. 

The  deposition  of  the  small  quantities  of  galena  occurred  chiefly 
through  the  replacement  of  the  arsenopyrite,  for  we  find  the  galena 
characteristically  cutting  across  the  arsenopyrite  and  possessing 
included  fragments  of  the  arsenopyrite.  and  at  the  same  time  .showing 
a  pronounced  tendenc\'  to  assume  its  cubical  crystal  form. 

The  deposition  of  the  gold,  the  last  of  the  metallic  minerals  to  form, 
was  accomplished  largely  by  the  replacement  of  previously  formed 
minerals,  chiefly  the  galena  and  to  a  lesser  extent  the  arsenopyrite  and 
pyrite.  Where  the  replacement  has  been  inconq)lete  small  areas  of 
these  minerals  may  be  observed  under  the  microscope  imbedded  in  th(; 
gold.  In  other  eases  small  grains  of  gold  are  imbedded  in  the 
sulphides — an  early  stage  of  the  rei)lacement. 

'I'he  last  miiuM-al  to  form  was  calcite.  occurring  in  more  or  less  open 
fractures  cutting  across  all  the  other  minerals  of  the  depasits. 

For  many  of  the  veins  the  original  fractures  were  insignificant  in 
^he  so  that  no  localized  deposition  of  vein  matter  could  occur.     In  these 


—  86  — 

cases  the  solutions  spread  out  through  the  minute  fractures  present  in 
the  rock  mass  adjacent  to  the  main  fracture,  and  succeeded  in  mineral- 
izing the  whole  rock. 

In  this  process  three  distinct  effects  may  be  recogijized,  though  some- 
what imperfectly.  The  first  of  these  is  the  leaching  of  the  rock  mass 
and  the  total  or  partial  destruction  of  many  of  the  minerals  originally 
present  in  it.  Those  which  appear  to  have  suffered  most  were  the 
ferromagnesian  minerals  which  were  in  most  places  completely 
destroyed,  and  the  feldspars  which  were  very  badly  altered. 

The  second  and  prol)al)ly  the  most  important  effect  was  the  deposi- 
tion of  new  minerals  along  the  fractures.  Numerous  tiny  quartz  vein-; 
lets  were  developed  forming  a  close  network  through  the  rock  mass.  I 
These  veinlets  show  a  well-developed  comb  structure  and  abundant 
small  drusy  cavities  into  which  the  minute  quartz  crystals  project. 
Abundant  pyrite  and  arsenopyrite  in  very  small  crystals  was  also 
deposited  along  these  fractures  in  connection  with  the  quartz  veinlets. 

The  third  effect  whose  relative  importance  is  somewhat  hard  to  gauge,: 
was  the  replacement  of  many  of  the  original  minerals  of  the  rocks  by 
other  minerals.     Certain  it  is  that  some  replacement  took  place  for  we 
now  find  pyrite,  arsenopyrite  and  gold  developed  locally  within  the 
rock  mass  quite  independent  of  the  fractures  Avhieh  may  be  present. 

Locally  the  mineralizing  solutions  appear  to  have  contained  nothing 
but  gold,  iron,  sulphur  and  arsenic,  for  much  of  the  ore  mined  in  the 
region  has  consisted  of  iron-stained  schist  which  has  been  impregnated 
with  gold  through  a  zone  of  varying  width  bordering  a  fracture.  No 
trace  of  ({uartz  or  other  introduced  vein  matter  other  than  that  inherent 
from  the  original  schist  is  present  in  such  eases.  The  stains  of  the 
iron  oxides  have  resulted  from  oxidation  of  pyrite  and  areenopyrite, 
originally  deposited  with  the  gold. 

OXIDATION   AND   ENRICHMENT. 

Practically  all  of  the  gold  ores  which  have  been  mined  in  the  quad- 
rangle have  been  oxidized  ores.  In  only  a  few  mines  have  the  primarj'^ 
sulphide  ores  been  encountered,  and  in  practically  every  case  they  have 
been  of  too  low  grade  to  work.  One  of  the  notable  exceptions  appears 
to  have  been  the  Sunshine  Mine  where  high-grade  ores  were  mined 
which  apparently  contained  primary  sulphides. 

While  noticeable  differences  do  exist  in  the  grade  of  the  oxidized  ores 
which  have  been  mined  as  contrasted  with  most  of  the  known  primary 
ores,  this  difference  is  not  believed  to  be  due  to  any  effect  of  enrich- 
ment of  the  oxidized  ores  in  general,  but  rather  to  the  fact  that  true 
primary  ore  shoots  have  not  been  discovered  outside  of  a  few  cases. 

The  grade  of  the  primary  sulphide  ores  which  have  been  encountered 
has  varied  somewhat  widely.  Important  bodi'^s  of  low-grade  sulphide 
ore  occur  south  of  the  Foot  wall  P'ault  in  the  Yellow  Aster  Mine.  The 
sulphides  occur  in  connection  with  veinlets  of  quartz  filling  a  network  of 
fractures  throughout  the  rock  mass.  The  rock  as  a  whole  is  said  to 
average  several  dollars  per  ton  in  gold  although  the  sulphides  themselves 
carry  gold  only  to  the  extent  of  about  $10.00  per  ton  of  concentrates. 
Apparently  much  of  the  gold  present  in  the  rocks  is  not  contained  in 
the  sulphides.  The  value  of  this  unoxidized  rock  is  quite  comparable  to 
the  value  of  the  oxidized  ore  which  has  been  mined  excepting  only  the 


PLATE   21. 


A.  THIN  SECTION  OF  GOLD-BEARING  VEIN  MATTER.  From  the 
Black  Hawk  Mine.  All  material  in  the  section  is  quartz.  Note  how 
the  small  crystals  control  the  boundaries  of  the  large  crystals.  50 
dia.    X  nicols. 


B.    GOLD    ORE    FROM    THE    SUNSHINE    MINE.       Galena    replacing 
arsenopyrite.     G  =  galena;  A  =  arsenopyrite  ;  Q  =  quartz.     40  dia. 


37841— facing  p.  86. 


—  87  — 

richer  veins,  none  of  which  have  been  discovered  in  the  unoxidized 
portion  of  the  deposit. 

In  the  JMonarch  Rand  workings,  assays  of  a  recently  discovered  vein 
of  unknown  extent  wliich  had  not  l)oon  oxidized,  indicate  a  gold  content 
of  al)out  $14.00  per  ton  according-  to  tlie  mine  superintendent. 

The  ore  of  the  Sunshine  Mine,  much  of  which  contained  primary 
sulphides,  is  said  to  have  run  well  over  $25.00  per  ton  in  gold. 

Quite  recently  a  small  rich  shoot  of  gold  ore  was  discovered  at  a 
de])th  of  about  150  feet  on  the  Oney  Lease  in  a  vein  cai-rying  primary 
sulphides.  The  vein  was  said  to  carry  about  $50.00  to  $75.00  per  ton  in 
gold  across  a  width  of  three  feet,  locally  l)eing  much  richer. 

These  examples,  though  few  in  number,  indicate  a  wide  range  in 
the  gold  content  of  tlie  primary  ores,  a  range  wide  enougli  to  account 
for  the  values  of  most  of  the  oxidized  ores  which  have  been  worked, 
and  making  unnecessary  any  postulation  of  secondary  enrichment  as 
an  important  agent  affecting  the  deposits. 

Gold  is  not  ordinarily  believed  to  be  subject  to  secondary  enrichment 
except  in  the  presence  of  manganiferous  solutions.  This  being  true,  the 
absence  of  manganese  minerals  may  be  accepted  as  further  evidence  of 
the  primary  nature  of  the  gold  even  though  the  ore  has  been  oxidized. 
Notal)le  exceptions  to  the  foregoing  statements  may  have  occurred  in 
certain  of  the  surface  ores  mined  in  the  early  days  from  the  Yellow 
Aster  and  otlier  properties.  These  ores  are  reputed  to  have  been  very 
rich  and  to  have  occurred  right  at  the  surface,  suggesting  an  enrich- 
ment, not  by  means  of  solutions,  but  through  a  downward  mechanical 
migration  and  concentration  of  small  fragments  of  gold  set  free  by 
processes  of  erosion,  the  downward  migration  of  the  gold  being  depend- 
ent on  its  own  weight. 

The  deptli  to  which  oxidation  extends  appears  to  be  quite  variable  in 
different  properties  and  is  apparently  controlled  very  largely  by  local 
conditions.  The  majority  of  the  gold  workings  are  only  a  few  hundred 
feot  deep  or  less  and  for  the  most  part  show  no  trace  of  the  primary 
sulphides,  though  in  a  few  mines  these  sulphides  begin  to  appear  at 
depths  of  from  200  feet  down.  In  other  properties  the  sulphides  are 
encountered  at  much  shallower  depths,  sometimes  more  or  less  inter- 
mingled with  oxidation  products.  In  a  few  cases  sulphide  and  oxidized 
ores  are  known  to  occur  side  by  side  as  the  result  of  faulting.  In  the 
Yellow  Aster  Mine,  the  ores  south  of  the  Footwall  Fault  on  the  Rand 
level  are  entirely  primary;  north  of  the  fault  oxidized  ores  are  known 
to  extend  downward  for  at  least  300  feet  below  the  Rand  level. 

The  oxidized  ores  show  a  very  wide  range  in  their  gold  content.  It 
would  be  extremely  difficult  if  not  impossible  to  strike  an  average  value 
for  those  ores  which  have  been  mined.  All  qualities  of  ore  have  been 
taken  out  fi'om  that  mined  in  the  Yellow  Aster  glory  hole  which  is  said 
to  average  from  $1.00  to  $1.25  per  ton,  to  extremely  rich  stringers  which 
have  in  some  cases  carried  hundreds  if  not  thousands  of  dollars  worth 
of  gold  per  ton. 

The  values  are  extremely  erratic  even  within  the  same  orebody,  so 
that  it  seems  probable  that  the  quantity  of  these  very  high-grade  ores 
which  have  been  mined  has  been  comparatively  small,  being  confined 
to  occasional  small  bunches.  The  distribution  of  the  values  in  the  ores 
has  in  general  been  so  erratic  that  in  most  mines  it  has  been  almost 
impo.ssible  to  maintain  any  appreciable  ore  reserves.     In  consequence 


—  88  — 

most  of  the  mines  have  led  a  hand-to-moiith  existence.     The  leasing 
system  has  been  qnite  popnlar  for  the  same  reason. 

The  o-old-silver  ratio  in  most  of  the  ores  appears  to  be  e(iually  erratic. 
Tims  in  tlie  ores  of  the  YcHow  Aster  Mine,  the  average  gold-silver  ratio 
according  to  IMr.  G.  W.  Nicholson,  the  snperintendent  of  the  property, 
has  been  only  about  >!?;■). 00  in  silver  to  .$1000.00  in  gold.  These  figures 
are  based  on  the  mint  returns.  In  contrast  to  this,  the  gold  obtained 
from  the  King  Solomon  IMine  is  worth  only  from  .$15.00  to  $16.00  an 
ounce,  running  from  780  to  780  in  fineness,  and  that  from  the  Black 
TIawk  runs  from  about  730  to  750  in  fineness. 

AGE   AND  GENESIS  OF  THE   DEPOSITS. 

The  age  of  the  gold  mineralization  can  be  fixed  fairly  closely  as  being 
early  Fpi)er  Pliocene  and  slightly  later  than  the  scheelite  mineralization. 
Tlu^  gold  deposits  are  known  in  many  places  to  cut  rhyolitic  and  diabase 
intrusives  which  are  definitely  of  early  Upper  Pliocene  age.  The 
similarity  in  the  areal  distribution  shown  by  these  intrusives  and  the 
gold  deposits  suggests  a  very  close  genetic  relationship. 

A  close  relationship  with  the  scheelite  deposits  is  shown  by  the 
common  direction  of  strike  of  many  of  the  gold  and  scheelite  veins,  by 
the  ])resence  of  scheelite  in  many  of  the  gold  veins  and  by  the  presence 
of  at  least  one  gold  pocket  in  a  .scheelite  vein.  In  addition  we  find  at 
least  one  gold  vein  in  the  midst  of  the  scheelite  belt,  possessing  a  strike 
parallel  to  the  other  veins  of  that  belt. 

The  scheelite  mineralization  is  known  to  l)e  slightly  the  older  for  in 
the  Union  ISUne  a  diabase  dike  is  reported  as  cutting  the  scheelite  veins 
while  in  no  case  is  a  diabase  dike  known  to  cut  a  gold  vein,  the  reverse 
always  being  true.  The  scheelite  present  in  the  gold  veins  is  believed 
to  be  the  last  effect  of  the  scheelite  mineralization. 

The  depth  of  formation  can  be  fixed  fairly  accurately  since  the  thick- 
ness of  the  Rosamond  series  present  when  the  diabase  was  intruded  is 
known  within  fairly  close  limits.  For  most  of  the  gold  deposits,  not 
over  a  few  luindred  feet  of  erosion  has  taken  place  since  the  period  of 
miuei-alizatiou,  while  in  many  cases  the  amount  of  erosion  has  probably 
been  somewlmt  less. 

It  follows  therefore  that  these  deposits  were  formed  in  immediate 
association  with  the  surface  and  hence  under  conditions  of  relatively 
low  t(Mnperatures  and  pressures.  It  is  interesting  to  note  that  the  ore 
textures  are  clearly  indicative  of  these  conditions  of  origin,  quite 
independent  of  the  field  evidence.  The  deposition  is  considered  to  have 
resulted  from  hot  ascending  allvaline  solutions  which  were  genetically 
related  to  the  deep-seated  magmatic  reservoir  from  which  the  rhyolitic 
and  diabasie  intru.sives  were  derived.  The  exact  composition  of  these 
solutions  can  only  be  inferred,  but  they  must  have  carried  silica,  gold, 
iron,  sulphur,  arsenic  and  lead  and  possibly  traces  of  copper,  zinc  and 
tellui-inni. 

STRUCTURAL  CONTROL  OF  THE  ORE  DEPOSITION. 

In  at  lea.st  one  of  the  gold  deposits,  namely  in  the  Yellow  Aster  ]Mine, 
a  sti'uctural  control  of  the  de{)Osition  of  the  gold  ores  can  be  demon- 
strated. 

In  this  property  part  of  the  mineralization  occurs  along  a  series  of 
vei-tical  fractures  having  a  northwest  .strike.     These  fractures  terminate 


FAULT   SYSTEM. 

or-     THE 

YELLOW  ASTER  MINE 

^^ Veins    and  Minerdlized  Zones 

O'  400' 


Figure  4 


37S41 — faring  n.    SS. 


—  88  — 

most  of  the  mines  have  led  a   liand-to-moiith  existence.     The  leasing 
system  has  ))een  quite  popular  for  the  same  reason. 

Tlie  sold-silver  ratio  in  most  of  the  ores  appears  to  ])e  ecfually  erratic. 
Thus  ill  Ihe  ores  of  the  Yellow  Aster  Mine,  the  average  gold-silver  ratio 
according  to  Mr.  G.  W.  Nicholson,  the  superintendent  of  the  property, 
has  been  only  about  $5.00  in  silver  to  $1000.00  in  gold.  Tlieso  tigures 
are  based  on  the  mint  returns.  In  contrast  to  tliis,  the  gold  obtained 
from  the  King  Solomon  ]\line  is  worth  only  from  $15.00  to  $16.00  an 
ounce,  running  from  780  to  780  in  fineness,  and  that  from  the  Black 
TIawk  rui7s  from  about  780  to  750  in  fineness. 

AGE  AND  GENESIS  OF  THE   DEPOSITS. 

The  age  of  the  gold  mineralization  can  be  fixed  fairly  closely  as  being 
cai-ly  T'^ppci-  INIiocene  and  slightly  later  than  the  seheelite  mineralization. 
The  gohl  deposits  are  known  in  many  places  to  cut  rhyolitic  and  diabase 
intrusives  which  are  definitely  of  early  Upper  Miocene  age.  The 
similarity  in  the  areal  distribution  shown  by  these  intrusives  and  the 
gold  deposits  suggests  a  very  close  genetic  relationship. 

A  close  relationship  with  the  seheelite  dei)Osits  is  shown  by  the 
common  direction  of  strike  of  many  of  the  gold  and  seheelite  veins,  by 
the  presence  of  seheelite  in  many  of  the  gold  veins  and  by  the  presence 
of  at  least  one  gold  pocket  in  a  .seheelite  vein.  In  addition  we  find  at 
least  one  gold  vein  in  the  midst  of  the  seheelite  l)elt,  possessing  a  strike 
parallel  to  the  other  veins  of  that  belt. 

The  seheelite  mineralization  is  known  to  l)e  slightly  the  older  for  in 
the  Union  Mine  a  diabase  dike  is  reported  as  cutting  the  seheelite  veins 
while  in  no  case  is  a  diabase  dike  known  to  cut  a  gold  vein,  the  reverse 
always  lieing  true.  The  seheelite  present  in  the  gold  veins  is  believed 
to  be  the  last  effect  of  the  seheelite  mineralization. 

The  depth  of  formation  can  l)e  fixed  fairly  accuratel.v  since  the  thick- 
ness of  the  Rosamond  series  present  when  the  diabase  was  intruded  is 
known  within  fairly  close  limits.  For  most  of  the  gold  deposits,  not 
over  a  few  hundred  feet  of  erosion  luis  taken  place  since  the  period  of 
minei'alizatiou,  while  in  many  cases  the  amount  of  erosion  has  probably 
been  somewhat  less. 

It  follows  therefore  that  these  deposits  were  formed  in  inunediate 
association  with  the  surface  and  hence  under  conditions  of  relatively 
low  temperatures  and  pressures.  It  is  interesting  to  note  that  the  ore 
textui'es  are  clearly  iutli^-ative  of  these  conditions  of  origin,  (piite 
independent  of  the  field  evidence.  The  deposition  is  considered  to  have 
resulted  from  hot  ascending  alkaline  solutions  which  were  genetically 
I'ehited  to  the  deep-seated  magmatic  reservoir  from  which  the  rhyolitic 
and  (liabasie  intrusives  were  derived.  The  exact  composition  of  these 
solutions  can  only  be  inferred,  but  they  must  have  carried  silica,  gold, 
iron,  sulphur,  arsenic  and  lead  and  possibly  traces  of  copper,  zinc  and 
tellurium. 

STRUCTURAL  CONTROL  OF  THE  ORE  DEPOSITION. 

In  at  least  one  of  the  gokl  deposits,  namely  in  the  Yellow  Aster  ]\Iine, 
a.  structural  control  of  the  deposition  of  the  gold  ores  can  l)e  demon- 
strated. 

In  this  property  part  of  the  mineralization  occurs  along  a  series  of 
vei'tical  fi'aetures  having  a  northwest  strike.     These  fractures  terminate 


FAULT   SYSTEM. 

OF      THE 

YtLLOW  ASTER  MINE 

m  Veins    and  Minerdlized  Zones 

o'  .  400' 


;7S41 — facing  p. 


11 
.s 

1 

a 
h 
a 
f] 
o 
T. 


Pc 

T 
ir 

si 
g( 

ec 
th 
of 
le; 

th 
\y] 
al- 
to 

ne 
kn 
ov 
mi 
bei 

as^ 
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te> 
inc 
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rel 
aiK 
sol 
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tell 


7 

a  s 

str; 

I 

ver 


—  89  — 

upwards  and  to  the  north  against  a  purved  fault  (probably  two  faults) 
which  is  termed  the  Jupiter  P^ault  where  it  strikes  east,  approx- 
imately, and  the  Ilantrins;  Wall  Fault  after  it  swings  around  and  strikes 
X.  W  W.  The  .Inpiter  P'ault  dips  from  40^  to  50°  to  the  north;  the 
Ilangin*;  Wall  Fault  dips  at  about  the  same  angle  to  the  northeast. 
The  footwall  of  these  faults  also  forms  a  mineralized  zone  varying  in 
thickness  frc.m  a  few  inches  to  as  nnieh  as  40  feet. 

^  These  iniiicralizcd  zones  which  pos.sess  the  Jupiter  and  Hanging  Wall 
Faults  for  tiicir  hanging  walls  reach  their  most  imi)ortant  development 
ahmg  the  trough  formed  by  the  sharp  bend  of  the  fault  and  in  those 
portions  which  are  above  the  intersections  of  the  mineralized  vertical 
fractui-es.  In  innn\-  cases  old  stopes  show  that  the  mineralization 
coming  up  a  verti<-al  fracture  actually  turned  and  followed  the  fault 
ai)ove  the  point  where  the  fracture  terminated. 

In  other  words  there  existed  here  at  the  time  the  gold  ores  were  being 
deposited  a  structural  trap  which  served  to  retard  all  the  ascending 
solutions  with  the  result  that  they  deposited  their  load  of  min(n-al 
matter.  Solutions  a.scending  the  vertical  fractures  were  halted  before 
reaching  the  fault,  depositing  the  materials  thev  carried  chiefly  near 
the  top  of  the  fracture  or  below  the  overlying  fault.  In  part  also  the 
solutions  were  forced  to  spread  out  throno-ji  the  adjacent  rock  mass 
there  to  develop  new  minerals.  ' 

And  in  consequence  we  find  orebodies  developed  which  reach  their 
maximum  size  and  also  terminate  immediately  ])elow  the  low-dipping 
pre-mincral  faults,  antl  we  tind  these  orebodies  gradualh-  decreasing'  in 
.size  with  depth,  in  some  cases  actually  feathcfing  out  downward  within 
the  limit  of  the  mining  operations  which  have  alreadv  been  carried  on 

Ihe  Jupiter  Fault  and  Hanging  AVall  Fault  have  long  been  regarded 
as  post-mineral  faults,  the  orebodies  immediatelv  beneath  being  con- 
sidered to  be  drag  orebodies  formed  from  brecciated  ore  derived  from 
the  tops  of  the  vertical  veins.  The  material  in  the  orebodies  under- 
lying the  Jupiter  P'ault  however  consists  chiefly  of  a  mineralized  country 
i-ock.  111  part  quartz  monzonite  and  in  part  schist.  Where  schist  form's 
the  rock  mas.s,  the  unbroken  schistosity  can  be  traced  to  sometimes 
withu,  a  tew  inches  of  the  fault,  even  though  the  mineralized  zone 
may  he  1.)  to  20  feet  thick.  This  unbroken  .schistositv  present  in  the 
inmeralized  zones  manifestly  rules  out  aiiv  i)ossibilitv  "of  the  ore  bein^^ 
l)reeciated  material  dragged  along  l)y  the  faulting.  '^ 

A  somewhat  similar  condition  on"  a  small  scal7  was  observed  in  tlie 
Silver  I,asin  workings  Here  a*  vertical  fracture  occurs  which  is  cut 
oft  by  a  low-dippmg  fracture.  The  vertical  fracture  and  the  upper 
part  of  the  low-dippmg  fracture  showed  the  presence  of  a  small  (luantitv 
of  gold  on  panning.  Figure  6  indicates  the  relative  positions  of  the 
tractures,  the  dots  representing  the  di.striliution  of  gold  in  a  rou'>-hlv 
jinantitative  manner.  No  gold  was  present  in  the  low-dippin-'  fractur'e 
hclow  Its  intersection  with  the  vertical  fracture.  Appar^ntlv  the 
deposition  of  the  .small  amounts  of  gold  was  dependent  on  the  slowin- 
np  of  the  solutions  which  were  ascending  along  the  vertical  fracture 
when  they  reached  the  intersection  with  the  low-dippino-  f,.;,cture 
1  he  arrows  indicate  the  line  of  movement  of  the  .solutions 

ihe  common  tendency  of  the  gold  vein.s  of  this  region  to  possess  a 
well  developed  hanging  wall  of  low  dip,  the  result  of  pre-nnneral  fault- 
ing, IS  believed  to  ],e  but  another  expres-sion  of  the  ^.tructural  control 


—  90 


z:' 


(0 


OS 

o 


—  91  — 

of  ore  deposition,  the  fault  p:onge  forcing  the  solutions  to  follow  beneath 
the  fault,  while  the  low  inclination  resulted  in  the  partial  stagnation 
of  the  solutions  and  consecjuent  ore  deposition. 

FUTURE  POSSIBILITIES  OF  GOLD   MINING. 

Certain  of  the  observations  which  have  been  made  appear  to  be 
especially  suggestive  as  regards  the  future  possibilities  of  gold  mining 
in  the  Raudsl)urg  quadrangle. 

Of   prime   importance   is   the   conclusion   reached   that  the   valuable 
siioots  of  oxidized  ore  wliich  have  been  mined  have  apparently  resulted 
from  primary  mineralization  without  noticeable  assistance   (except  at 
the  immediate  surface)    of  processes  of  secondary  enrichment.     This 
conclusion  is  of  importance  in  that  it  immediately  follows  that  primary 
ores  may  be  found  as  the  result  of  future  prospecting  which  may  be 
as  rich  as  any  of  the  oxidized  ores  which  have  been  mined  in  the  past. 
A  consideration  of  the  deeper  portions  of  the  known  deposits  does 
much  to  otlt'set  this  favorable  feature,  however.     In  no  case  known  to 
the  writer  have   rich  ores  persisted 
beyond  a  depth  of  a  few  hundred  feet. 
In  the  deepest  gold  mine  of  the  dis- 
trict, the  Sunshine  Mine,  the  vein  was 
followed  to  a  depth  of  about  600  feet 
where  the   values   apparently   disap- 
peared.   In  the  Yellow  Aster  Mine  the 
orebodies  on  the  third  level  were  too 
small  and  low  grade  to  work.  The  Yel- 
low Aster  orebodies  show  a  gradual  de- 
crease in  size  from  the  top  do\niward. 
In  the  ma.joritv  of  the  smaller  prop-      figure  6.  structural  control  of  min- 

Pvtip<i     of     flip     fiktript     thf.     viVh     nrp    eralization    by    solutions    ascending    a 
eUies     or     tne     CnsniCt     tne     licn     ore    vertical  fracture.  Arrows  indicate  prob- 

shootS  have  been  exhausted  at  depths    able    flow    of    solutions.     Dots    indicate 

of  from  100  to  300  feet.  '•^^^^'^'^  distribution  of  gold. 

Since  the  gold  deposits  have  formed  in  close  association  with  the 
present  surface,  the  shallow  extent  of  the  known  ore  shoots  is  believed 
to  be  characteristic  of  the  gold  mineralization.  This  being  true,  it 
would  follow  that  the  possibilities  for  the  occurrence  of  orebodies  near 
the  surface  would  l)e  several  times  as  great  as  the  possibility  of  their 
occurrence  at  depths  greater  than  several  hundred  feet.  While  the 
possibility  of  finding  deeper-seated  orebodies,  blind  veins  or  segments 
of  veins  buried  by  faulting  can  not  be  denied,  the  writer  does  not 
believe  that  deep  exploration  work  is  .justified  unless  an  orebody  is 
actually  being  followed  or  unle.ss  special  structural  conditions  suggest 
the  advisability  of  such  deep  exploration. 

Perhaps  one  of  the  best  possibilities  in  the  district  is  to  be  found  in 
the  loss  through  faulting  of  portions  of  orebodies  of  known  value. 
The  presence  of  such  faulted  orebodies  offers  an  inducement  for  more 
detailed  geologic  work  than  has  as  yet  been  attempted.  Search  for 
such  faulted  segments  should  not  be  undertaken,  however,  unle.ss  it  can 
be  definitely  shown  that  the  deposit  is  actually  faulted  off  and  not 
bounded  by  a  pre-miueral  fault. 


92 


PLATE  22. 


A.  STOPE  AT  TOP  OF  THE  RAXD 
VEItTICAL,  VEIN,  YELLOW 
ASTER  MINE.  Shows  the  over- 
tiiiniiis  of  the  vein  caused  by  the 
structural  control  of  the  ore 
deposition, 


SILVER  DEPOSITS. 

FIELD   RELATIONS. 

At  first  glance  the  silver  mineral- 
ization appears  to  be  fairly  limited 
ill  extent.  Commercial  production 
of  silver  ores  has  been  practically 
limited  to  a  single  mine,  the  Cali- 
fornia Rand  Silver  Mine,  though 
several  small  shipments  of  ore  have 
been  made  from  the  Silver  King 
])roi)erty,  and  similar  sliipments 
eould  prol)ably  have  been  made 
from  the  Coyote  ground. 

While  the  area  covered  by  these 
properties  appears,  so  far  as  infor- 
mation is  now  available,  to  be  the 
limit  of  the  eeonomicall.v  valuable 
deposits,  the  mineralization  proper 
is  niiueli  more  widespread  so  that 
iiuu'li  of  the  adjacent  territory  is 
felt  to  ]iossess  at  least  a  potential 
value.  Intensive  deep  prospecting 
lias  already  disproved  much  of  this 
possible  silver-producing  territory, 
however. 

So  far  as  prospecting  operations 
have  made  information  available, 
the  area  in  which  the  silver-bearing 
solutions    were   active    appears   to 


B.  THE  'SILVER  CAMP"  FROM  THE  EAST.  The  prominent  liills  are  com- 
posed of  silicified  Rosamond  strata  overlying  quartz  monzonite,  the  one  at 
the  right  being  intruded  by  a  rhyolite  neck. 


—  93  — 

be  limited  on  the  west  by  the  vein  being  prospected  by  the  workings 
of  the  St.  Lawronce  Rand  and  Baltic  properties,  wliile  on  the  south 
the  hoklings  of  tlie  Pittshnru:  and  Mt.  Shasta  Mining-  Coiiipany  rougidy 
limit  the  area.  The  limits  to  the  north,  northea.st  and  east  can  not 
be  definitely  fixed  due  to  the  cover  of  Rosamond  sediments  and  later 
voh-anics  l)eneath  whieli  the  (h'posits  ])ass.  Traces  of  silver  mineraliza- 
tion are  known  to  occur  in  the  North  Kand  District,  north  of  Red 
Mountain,  thoutrii  whethei*  tiiey  represent  an  extension  of  the  same 
area  of  mineralization  as  that  in  which  the  known  deposits  are  located, 
or  whether  they  form  an  outl.xim^  and  distint'tly  sejnjrate  area  has 
not  as  yet  been  demonstrated.  Nor  have  intensive  i)rospecting  opera- 
tions in  the  North  Rand  District  ilisclosed  any  definite  possil)ilities  of 
connnercial  nuneralization  having  occurred. 

The  silver  mineralization,  whether  of  commercial  value  or  otherwise, 
has  occurred  chietly  in  the  Rand  Schist,  hut  is  also  known  to  have 
effected  the  (piartz  monzonite,  certain  portions  of  the  Ro.samond  Series 
and  both  the  diahasic  and  i-h\-olitic  intrusive  igneous  rocks  of  early 
rppei-  Pliocene  age. 

All  of  the  economically  valuable  orcl)o(lii's  which  have  yet  been 
discovered  have  been  in  the  Rand  schist.  This  has  been  purely  a 
matter  of  chance,  however,  dejiendent  on  local  structure  favorable  for 
deposition  and  quite  independent  of  the  nature  of  the  schists  them- 
selves. Valuable  orebodies  are  just  as  apt  to  occur  in  the  cpiartz 
monzonite  as  they  are  in  the  schist,  other  things  being  eciual.  The 
intrusive  igneous  rocks  of  Miocene  age  in  general  occur  in  masses 
too  small  in  extent  to  serve  in  themselves  as  sites  of  orebodies,  though 
locall.v  the,v  are  known  to  l)e  mineralized  or  to  serve  as  wall  rocks  for 
the  silver-bearing  veins. 

The  lower  beds  of  the  Rosamond  series,  while  locally  mineralized, 
are,  believed  to  have  been  too  porous  to  have  allowed  of  the  forma- 
tion of  valuable  orebi)dies.  silvei-  heai'ing  solutions  entering  them  most 
probably  l)eing  immediately  dissipated  through  a  wide  area. 

The  bluish-gray  color  of  the  schists  encountered  in  the  silver  mining 
operations  has  locally  led  to  the  belief  that  they  were  a  distinct  fornui- 
tion  differing  from  the  outer  schists  of  the  region.  The  term  'Silver 
Formation'  has  locally  been  applied  to  these  bluish-gray  schists.  They 
are,  however,  part  of  the  Rand  schists  and  do  not  dift'er  from  the  schists 
present  in  other  i)ortions  of  that  terrain.  In  most  of  the  mining 
operations  previous  to  the  silver  discovery  in  1!)19,  the  mine  openings 
were  not  deep  enough  to  penetrate  through  the  zone  of  oxidation. 
And  in  this  zone  the  schists  are  ordinaril.v  soft  and  ])rownish-gra.v  in 
color  due  to  the  effects  of  oxidation.  The  deep  prospecting  following 
the  silver  discovery  was  largely  carried  on  in  hard  unoxidized  schists 
in  which  the  original  color  was  apparent.  The  most  common  schist 
encountered  in  the  silver  mining  operations  has  been  a  ndca-albite 
schist,  though  at  certain  horizons  (|uartzites  and  amj)hil)(ili'  schists 
have  been  recognized.     (See  Plate  8-A.) 

The  schists  exposed  in  the  California  Rand  Silver  ^Mine  and  in  the 
workings  of  adjacent  properties  are  slightl,v  rolling  in  attitude  and 
appear  to  possess  a  general  low  dij)  to  the  southeast,  usuall.v  not  over 
twenty  degrees.     Locall.v  reverse  dips  occur. 

Diabase  intrusives  have  been  enconntered  in  certain  of  the  workings, 
most  notably  in   the   workings   off  the   California    Rand   Number   Six 


—  94  — 


Grad^  5hof+ 


—  95  — 

shaft,  in  the  Fox  Lease  workinf?s  and  in  the  Mizpah  Montana  work- 
ings. These  intrusives  urdinarily  take  the  form  of  dikes,  but  are 
extremely  irregular.  They  are  usually  of  small  size  though  oue 
observed  on  the  600  foot  level  of  the  California  Rand  Number  Six 
shaft  was  rather  large.  It  was  badly  altered  adjacent  to  the  veins, 
and  was  cut  by  a  number  of  veinlets  carrying  traces  of  silver.  The 
mass  of  the  dike  aside  from  these  veinlets  also  shows  silver  on  analysis. 
The  workings  of  several  properties  cross  the  intriisive  contact  of  the 
quartz  monzonite  and  the  Rand  schist.  In  the  crosscut  from  the 
Fox  Lease  shaft  the  contact  was  cut  250  feet  from  the  shaft.  The 
workings  of  the  Mizpah  Montana  are  in  the  contact  zone,  at  times  being 
in  schist,  at  other  times  being  in  the  (piartz  monzonite.  The  only 
evidence  of  contact  metamorphism  observed  in  the  Mizpah  Montana 
workings  was  a  silicification  and  hardening  of  the  schist. 

STRUCTURE  OF  THE  DEPOSITS. 

The  silver  ores  occur  almost  entirely  in  definite  but  extremely 
complicated  veins.  Two  systems  of  veins  can  be  somewhat  imperfectly 
recognized,  an  earlier  set  which  for  the  most  part  strike  approximately 
N.  -40°  E.,  and  a  later  set  which  strike  roughly  north,  possibly  in  general 
a  little  west  of  north.  A  few  of  the  outlying  veins  may  possess  strikes 
which  do  not  agree  with  those  given  above.  For  example  the  vein 
being  prospected  by  the  St.  Lawrence  Rand  strikes  N.  62°  E. 

The  veins  of  both  the  northeast-southwest  series  and  of  the  north- 
south  sei'ies  in  general  dip  to  the  east  and  southeast,  steeply  near  the 
surface,  but  showing  flatter  and  flatter  dips  with  depth.  Average 
dips  for  the  upper  portions  of  the  veins  would  probably  be  around 
75  degrees,  while  the  dips  in  depth  appear  to  decrease  to  40  degrees 
or  less.  There  are  some  exceptions  to  this  general  statement,  however, 
for  a  few  veins  stand  vertical  near  the  surface  and  one  or  two,  as 
for  example  the  Alpha  and  Grady  Lease  Veins,  turn  over  in  their  upper 
part  and  show  a  westward  dip.     (See  Figure  7.) 

The  largest  veins  of  the  district  belong  to  the  northea.st-southwest 
system.  Of  the  many  known,  the  Footwall  Vein  is  the  largest,  and 
also  one  of  the  few  which  outcrop.  This  vein  is  exposed  on  the  sur- 
face for  a  distance  of  over  3500  feet,  standing  out  prominently  as  an 
important  topographic  feature.  It  varies  in  thickness  from  40  to  80 
feet,  pr()l)ably  averaging  aliout  50  feet.  It  passes  some  150  feet  to  the 
west  of  the  Number  One  Shaft  of  the  California  Rand  Silver  Mine, 
its  outcrop  terminating  a  few  hundred  feet  north  of  the  shaft.  It 
has  been  regarded  by  many  as  a  dike  and  has  been  described  as  such, 
but  it  is  a  vein  in  eveiy  sense  of  the  word  and  does  not  possess  a 
single  feature  whieli  even  suggests  an  igneous  rock.  The  Footwall  Vein 
does  not  differ  essentially  from  others  of  the  veins  except  in  its  silver 
content  which  is  too  low  to  allow  of  its  being  mined.  The  other  veins 
vary  in  thickness  from  the  maximum  figures  given  above,  down  to 
mere  fractures. 

The  veins  of  the  northeast-southwest  system  converge  with  depth, 
so  that  it  appears  probable  that  they  finally  join  and  form  trunk  veins. 

The  north-south  series  of  veins  are  for  the  most  part  fairly  short, 
being  limited  in  length  by  their  intersections  with  the  veins  of  the 


—  96  — 

earlier  system.  In  places  the  veins  of  the  two  systems  appear  to 
mer»e,  so  that  it  is  difficult  to  detect  any  difference  in  the  time  of 
their  formation ;  in  other  cases  the  north-south  veins  distinctly  cut 
those  of  the  otlier  system.  An  example  of  a  north-south  vein  cutting 
one  of  the  northeast-southwest  veins  may  he  observed  on  the  720  foot 
level  of  the  California  Hand  Number  Six  shaft  workings. 

The  north-south  veins  on  the  whole  are  prol)a])ly  somewhat  nar- 
rower than  those  of  the  othej-  system,  from  five  to  ten  feet  prol)ably 
being  an  average  thickness,  tliough  locally  they  may  be  over  thirtj^ 
feet  thick.  They  branch  and  form  intersections  among  themselves  as 
well  as  with  tlic  northeast-southwest  veins,  both  along  their  strike  and 
in  depth. 

Locally,  as  in  the  Number  8  Stope  of  the  California  Rand  Silver 
Mine,  instead  of  definite  veins  being  present,  the  entire  mass  of  the 
rock  may  be  cut  by  numerous  small  intersecting  veinlets,  so  that  the 
rock  as  a  whole  forms  good  ore. 

All  of  the  veins,  excepting  those  now  exposed  at  the  surface,  are 
terminated  upwards  by  a  flat-lying  fault  which  strikes  roughly  N.  30*^ 
E.,  and  dips  to  the  southeast  at  angles  of  about  HO  degrees  in  its  upper 
part,  flattening  out  to  dips  of  about  10  degrees,  however,  with  gi-eater 
depth.  It  is  probable  that  all  the  veins  were  once  covered  by  this  fault, 
those  now  exposed  being  so  as  the  result  of  erosion  of  the  overlying 
m;;tcrial.  This  fault  is  not  sharp  but  rather  a  crushed  zone  of  schist 
which  has  suffered  intense  movements.  The  crushing  is  so  ijitense 
that  ordinarily  all  the  features  of  the  original  schist  are  destroyed,  a 
thick  fault  gouge  being  formed  which  has  locally  been  termed  'the 
mud  wall.'  The  fault  plane  appears  to  l)e  not  a  simple  plane  but 
rather  a  warped  surface. 

This  fault  is  pre-mineral  and  forms  a  natural  capping  to  the  veins, 
none  of  the  veins  ever  having  extended  above  it.  Several  oi'  the 
ve-ns  appear  to  be  traceable  for  short  distances  into  the  fault  gouge, 
so  tliat  there  can  be  no  question  but  that  the  formation  of  the  veins 
j)ost dates  the  formation  of  the  flat  fault. 

The  top  of  the  TIarrell  Vein,  just  above  the  4th  level  of  the  Cali- 
fornia Rand  Silver  Mine,  was  observed  to  cut  through  and  slightly 
offset  some  of  the  lowest  planes  of  movement  connected  with  the  flat 
fault,  fhougli  small  later  movements  along  other  of  these  planes  in 
turn  offset  the  Ilarrell  Vein  for  .short  distances.  These  later  move- 
ments have  resulted  in  small  (pianfifies  of  brecciated  vein  matter  being 
spread  for  short  distances  through  the  fault  gouge.  The  gouge  itself 
is  in  places  mineralized,  small  crystals  of  pyrite  and  stibnite  being 
observed  which  had  certainly  never  l)een  subjected  to  movements  of 
any  kind. 

The  veins  may  show  sharp  boundaries  with  the  bordering  rocks  where 
faulting  has  developed  a  definite  wall,  but  more  commonly  the  \yalls 
of  the  vein  are  somewhat  indefinite  and  gradational,  due  either  to 
replacement  of  the  schist  through  varying  distances  adjacent  to  the 
fracture,  or  to  minor  fracture  systems  which  commonly  extend  out 
into  the  wall  rocks  from  the  nuun  fissure  which  have  been  filled  with 
vein  matter.  As  a  result  the  veins  may  swell  and  pinch  through  wide 
limits. 


PLATE   23. 


A.  VEIN  MATTER,  GTfT  LEVEL,  CALIFORNIA  RAXD  SILVER 
MINE.  Cryptocrystalline  silica  to  fine-grained  quartz  groundmass, 
with  larger  quartz  metasomes.    50  dia.    X  nicols. 


B.  VEIN  MATTER,  IITH  LEVEL,  CALIFORNIA  RAND  SILVER 
MINE.  Composed  of  cryptocrystalline  silica  to  fine-grained  quartz 
groundmass,  cut  by  a  coarsely  crystalline  veinlet  of  quartz  of  a 
later  generation.  The  center  of  the  quartz  veinlet  is  filled  with 
pyrite    (P).    54    dia.   X  nicols. 


37S4 — facing  p.  96. 


—  97  — 

NATURE  OF  THE  VEIN  FILLING. 
Mineralogy. 

QUARTZ.  Silica  in  some  form  coinpose.s  the  greater  portion  of  the 
gangue  pre.sent  in  the  veins.  Quartz  is  one  form  which  is  (piite 
ahuuclant  oceurrinjii'  chiefly  as  irreuuUir  grains,  micr()sc()[)ic  in  size  or 
hu'irer,  scattered  through  the  other  materials.  It  also  occurs  in  a  better 
crystallized  form  as  a  lining  to  narrow  fractures  and  open  drusy 
cavities  which  cut  the  or(\  wlicn  it  commoidy  possc^sses  a  comb  struc- 
ture and  shows  crystalline  terminations.  The  (piartz  is  usually  tpiite 
colorless. 

CHALCEDONY.  Much  of  the  vein  matter  consists  of  erypto- 
crystalline  to  i-sotropic  silica  which  cannot  be  resolved  under  the  micro- 
scoiH'  and  shows  no  illuminatioti  uiuhn-  crossed  nieols.  This  material 
is  believed  to  be  largely  chalcedony  though  some  opal  may  be  pre.sent. 
It  appears  bluish-gray  to  nearly  black  in  color  to  the  unaided  eye. 
Under  the  microscope  the  color  is  found  to  be  due  to  cloudy  inclu- 
sions whose  exact  nature  is  not  known,  liut  which  may  be  iron  oxides. 
This  cryptocrystalline  to  isotropic  silica  coimuonly  acts  as  a  ground- 
nujss  for  irregular  cpiartz  grains  of  various  sizes. 

ALLOPHANE.  Al.,0,.SiO,.nILO.  A  white  amorphous  hydrous 
mineral,  sometimes  opaline,  connnoidy  observed  in  small  amount  in  the 
silver  veins.  Isotropic.  n=1.48.  Infusible.  Largely  soluble  in  acid 
yielding  gelatinous  silicia.  Some  halloysite,  Al20y.2Si(),.nll20,  may 
be  present. 

CALCITB.  Occurs  in  white  crystalline  aggregates,  most  commonly 
lining  cavities.     One  of  the  last  minerals  to  form  and  not  abundant. 

MIARGYRITE.  AgSbS,.  Probably  the  most  abundant  silver 
mineral  present  in  the  deposits.  ^liargyrite  was  fii-st  identified  as 
occurring  in  this  region  by  Professor  A.  S.  Eakle.^  It  is  a  soft,  brittle, 
metallic  mineral,  lead-gray  to  ])lack  in  color  and  possesses  a  deep  red 
streak.  It  is  locally  termed  'ruby  silver'  although  the  true  ruby 
silver  is  i)roustite.  It  differs  slightly  from  pyrargyrite  in  composition 
and  crystal  form,  crystallizing  in  the  monoclinic  system.  Well-formed 
crystals  of  fair  size  are  frequently  found  in  the  open  drusy  cavities 
in  the  veins.  Ordinarily  miargyrite  is  considered  to  be  a  rare  mineral. 
In  the  polished  surface,  under  the  microscope,  miargyrite  was  observed 
to  be  noticeably  pleochroic,  varying  from  a  deep  lavender-gray  to 
light-gray  in  color. 

8TYL0TYPITE.  8(Cu,Ag,Fe)S.Sb,S,.  Oidy  slightly  less  impor- 
tant in  quantity  than  the  miargyrite.  The  presence  of  stylotypite  in 
the  ore  is  usually  not  apparent  in  the  hand  specimen,  since  it  ordina- 
rily occurs  in  minute  irregular  or  rounded  grains,  commonly  micro- 
scopic in  size,  which  are  usually  entirely  surrounded  by  miargvi'ite.  It 
is  almost  invarial)ly  associated  with  snmll  (|uantities  of  chalcopyrite 
and  occasionally  with  argentiferous  bornite  (  ?)• 

Stylotypite  is  a  silver-bearing  bournonite.  It  is  metallic,  dark  gray 
in  color,  ])rittle,  and  possesses  a  black  streak.  Identification  was  made 
froiu  small  selected  fragments  which  microscopic  examination  showed 
to  be  free  from  chalcopyrite  and  miargyrite.     Repeated  microchemical 

'A.   S.    Eakle.     Minerals  of   California.     Calif.    State   Min.   Bureau.      Bull   91,   p    70 
"  '7—37841 


—  98  — 

and  blowpipe  tests  showed  the  presence  of  copper,  silver,  iron,  antimony 
and  sulphur.  In  the  polished  surface  stylotypite  is  faintly  gray,  being 
slig-htly  lighter  in  color  than  the  miargyrite.  It  usually  shows  abundant 
minute  inclusions  of  quart/..  The  hardness  is  the  same  a,s  chalcopyrite 
(—3.0  to  3.5). 

PYRARGYRITE.  Ag.SbSs.  Similar  to  the  miargyrite  with  which 
it  occurs  intergrown  in  comparatively  small  amount.  Its  chief  dis- 
tinction from  the  miargyrite  is  in  its  lighter  color.  The  pyrargyrite 
is  also  noticeably  pleochroie  in  the  polished  surface,  varying  from  light 
gray  to  nearly  white. 

PROUSTITE.  Ag-jAsSg.  Present  in  the  ores  only  in  small  quantity. 
Easily  identitied  by  reason  of  its  bright  red  color,  semi-transparency 
and  brilliant  red  streak.     Proustite  is  the  true  'ruby  silver.' 

CERARGYRITE.  AgCl.  Commonly  termed  'horn  silver.'  Cerar- 
fiyrite  is  the  chief  secondary  silver  mineral  developed  in  the  deposits 
of  the  Randsburg  quadrangle.  Cerargyrite  is  a  stable  mineral  of  non- 
metallic  lustre,  waxy  in  appearance,  and  varying  in  color  in  the  ores  of 
the  California  Rand  Silver  Mine  from  creamy  yellow  through  various 
shades  to  steel  gray. 

BROMIDES.  Bluish-green  stains  observed  in  some  of  the  oxidized 
ores  have  been  termed  bromides,  but  have  not  been  definitely  identified 
as  such.  These  stains  may  possibly  be  due  to  the  traces  of  copper 
present  in  the  silver  ores. 

SECONDARY  SULPHIDES.  The  secondary  ores  have  been  almost 
completely  worked  out  so  that  specimens  containing  secondary  sulphides 
are  now  hard  to  obtain.  In  consequence  but  little  knowledge  of  the 
secondary  minerals  was  obtained,  and  (mly  a  few  samples  were 
examined.  It  seems  probable  tliat  some  stephanite  occurred  in  the 
upi)er  levels  of  the  (California  Rand  Silver  Mine,  possilily  accompanied 
by  other  secondary  sulphides. 

PYRITE.  FeS.^.  One  of  the  most  abundant  of  the  metallic  minerals 
present  in  the  silver  ores.  Occurs  in  very  minute  brassy  cubes  or 
crystalline  aggregates,  either  scattered  through  the  vein  matter  and 
wall  rocks,  or  cutting  either  in  narrow  veinlets. 

ARSENOPYRITE.  FeAsS.  Present  in  about  the  same  abundance  as 
the  pyrite.  Occurs  in  very  minute  crystals  or  crystal  aggregates  which 
are  only  slightly  lighter  in  color  than  the  pyrite.  Due  to  their  small 
size  they  are  distinguished  from  i)yrite  with  the  unaided  eye  only  with 
the  greatest  difficulty.  The  large  amount  of  arsenopyrite  present  in 
the  ores  accounts  for  the  high  arsenic  content. 

CHALCOPYRITE.  CuFeS^.  Present  more  or  less  uniformly 
through  the  ores  but  only  in  <'xtremely  ininute  quantities.  The 
chalcopyrite  is  apparent  only  uiuler  the  microscope.  The  quantity 
pres-ent  is  great  enough  to  account  for  the  bluish-green  stains  present 
ill  the  oxidized  ore  which  have  been  classed  as  bromides. 

ARGENTIFEROUS  BORNITE?  A  deep  purplish-brown  mineral, 
darker  in  color  than  ordinary  bornite,  occurs  associated  with  the  chalco- 
pyrite in  minute  rounded  grains  obsen^able  only  under  the  microscope. 
These  grains  were  too  small  to  test  by  micro-chemical  methods.     This 


—  99  — 

niintn'al  appears  to  correspoiul  to  a  mineral  desei-ihed  hy  J.  Mui-doeli' 
and  believed  hy  him  to  he  an  argentiferous  l)ornite. 

STIBXITE.  SboSy.  Occurs  in  long  prismatic  crystals,  sometimes 
radially  arranged,  or  as  a  massive  aggregate  filling  veinlcts.  In 
general  it  is  best  developed  in  the  leaner  ore.  Specimens  of  stihuite 
obtained  fn)m  the  Randsliurg  quadrangle  were  observed  to  be  noticeably 
pleochroic  in  the  polished  surface,  varying  from  white  to  light  gray  in 
color  a-s  seen  under  the  microscope  using  vertical  illumination. 

]\rARIPOBITE.  A  chromiferous  mica.  A  bright  green  flaky  mineral 
observed  at  several  places  in  the  outcrop  of  the  Footwall  Vein.  Not 
common. 

MELAXTERITE.  FeiS0,.7II.,0.  Occurs  locallv  in  snuill  amount 
as  an  efflorescent  coating  on  the  Avails  of  certain  of  the  workings  Avhich 
have  been  opened  for  several  years. 

GOLD.  All  of  the  silver  ores  carry  a  somewhat  variable  gold  content. 
The  mode  of  occurrence  of  the  gold  has  not  as  yet  been  determined  in 
general,  though  locally  in  the  California  Rand  Silver  ^line  specimens 
carrying  native  gold  have  been  found. 

GRADE  OF  THE  ORES. 

]\Iuch  of  the  silver  ore,  both  primary  and  secondary,  which  has  been 
mined  has  been  of  very  high  grade.  The  richest  ore  which  has  been 
mined  was  probably  that  from  the  Treasure  Box  Vein  on  the  3rd  level 
of  the  California  Rand  Silver  ]\Iine.  Some  of  this  ore  assayed  as  high 
as  13,000  oz.  of  silver  per  ton.  The  silver  here  occurred  chiefly  in  the 
form  of  cerargyrite  and  secondary  sulphides. 

Sucli  values  as  that  given  above  are  (luite  exceptional  for  the  major 
portion  of  the  ore  which  has  been  mined  would  range  from  10  to  300  oz. 
of  silver  per  ton.  The  average  for  all  the  ore  mined  to  date  roughly 
approximates  50  oz.  of  silver  and  $3.00  of  gold  per  ton. 

The  gold  values  are  quite  erratic,  no  definite  gold-silver  ratio  being 
recognized.  In  general  the  ratio  of  gold  to  silver  is  higher  in  the  lower 
grade  ores  than  in  the  rich  ores,  suggesting  that  the  gold  and  silver  have 
had  dift'erent  origins. 

The  arsenic  content  of  the  ores  is  noticeably  higher  than  the  antimony 
content,  despite  the  fact  that  most  of  the  primary  silver  minerals  cany 
antimony  but  no  arsenic.  Concentrates  carrying  300.  oz.  of  silver  per 
ton  assay  from  57f  to  6%  arsenic  and  only  2%  to  37o  antimony.  The 
arsenic  content  of  the  ores  is  probably  almost  wholly  derived  from  the 
arsenopyrite  present. 

The  best  ores  have  for  the  most  part  come  from  the  veins  of  the 
north-south  system,  the  richest  shoots  occurring  along  the  junctures  of 
these  veins  with  those  of  the  northeast-southwest  system. 

ORE  TEXTURES  AND  PARAGENESIS. 

Perhaps  the  most  characteristic  feature  of  the  ores  is  the  fine-grained 
to  aphanitic  gangue  which  varies  from  a  bluish-gray  to  a  dark  gray  in 
color.  This  gangue  material  usually  shows  a  more  or  less  delicate 
banding  as  the  result  of  slight  variations  in  color  or  granularity  of  the 

'J.  Murdoch.     Microscopical  Determination  of  thie  Opaque  Minerals,  p.   65. 


—  100  — 

material,  or  due  to  the  development  of  layers  of  metallie  minerak  in  it. 
Locally  l)ands  of  white  ({iiartz  are  present.  The  individual  bands  are 
((uite  variahh'  in  width,  many  heiny  very  thin,  others  being  coarse. 
They  may  either  parallel  the  walls  of  the  vein,  or  the  banding  may  be 
developed  around  inclusions  or  open  drusy  cavities. 

Inclusions  of  angular  schist  fragments  are  (juite  abundant  throughout 
the  veins.  These  inclusions  may  have  almost  knife-edge  corners  which 
show  no  trace  of  rounding.  They  are  derived  from  the  immediately  adja- 
cent wall  rocks,  and  hence  all  those  observed  by  the  \\Titer  were  composed 
of  schist.  The  fragments  are  oriented  with  their  schistosity  at  random 
in  any  direction.  They  vary  greatly  in  size,  from  minute  fragments  so 
small  as  to  be  hardly  recognizable  to  pieces  several  inches  across. 

Another  type  of  material,  namely  apparently  anuular  fragments  of 
white  ([uartz,  are  fairly  commonly  found  iml)edded  in  the  gray  silicious 
silver-bearing  vein  matter.  This  white  quartz  is  quite  similar  to  the 
quartz  which  forms  the  gangue  in  many  of  the  gold  veins.  These  frag- 
ments are  l)elieved  to  be  the  result  of  brecciatiou  of  earlier  gold  veins, 
the  brecciated  material  being  incorporated  in  the  later  developed  silver- 
])earing  veins. 

Open  drusy  cavities  are  extremely  common.  They  are  of  all  sizes, 
many  being  quite  small,  others  observed  being  nearly  a  foot  in  diam- 
eter l)y  several  feet  in  length.  A  special  type  of  cavity  commonly  seen 
is  a  Hat  open  space  occupying  the  centers  of  some  of  the  veins.  Such 
openings  represent  portions  of  the  veins  where  the  vein  filling  was 
not  comjileted. 

The  open  cavities,  whether  druses  or  unfilled  vein  centers,  are  lined 
with  small  crystals,  usually  of  white  quartz  with  pyramidal  termina- 
tions, but  in  .some  cases  by  coarser  crystals  of  calcite.  AVell  formed  and 
at  times  rather  large  crystals  of  miargyrite  and  occasionally  of  prou.st- 
ite  also  occur  rather  abundantly  growing  from  the  walls  of  these  cavities. 
In  the  larger  cavities  mammillary  and  stalactitic  fornLS  sometimes 
occur. 

^luch  of  the  vein  matter  has  been  badly  brecciated  and  crushed. 
Much  of  this  brecciated  material  instead  of  being  angular  as  might  be 
expected  is  distinctly  rounded.  In  many  cases  the  brecciated  material 
shows  but  slight  traces  of  later  eementation  so  that  the  vein  is  (piite 
porous  on  a  coarse  scale.  In  other  cases  these  fragments  are  incorpor- 
ated in  later  deposited  vein  matter.  Silver  minerals  may  occur  within 
these  fragments  but  are  mcst  abundant  surrounding  the  fragments.  The 
individual  fragments  range  in  size  up  to  as  much  as  a  foot  or  more  in 
diameter. 

Evidence  of  movement  is  also  found  in  slickensiding  and  the  develop- 
ment of  fault  gouge.  Such  planes  of  movement  may  locally  serve  as 
walls  to  the  vein,  or  they  may  cut  through  the  vein  niatter.  The  silver 
)ninerals  are  quite  commonly  .seen  to  be  crushed  and  to  show  the  effects 
of  slickensiding. 

The  \yalls  of  the  veins  ai-e  seldom  sharp  except  in  those  places  where 
the  po.sition  of  the  wall  has  l)een  controlled  by  a  plane  of  movement 
which  is  slickensided  and  po.s.sesses  a  fault  gouge.  Mucli  more  com- 
monly the  veins  pass  somewhat  indefinitely  into  the  wall  rock  and 
veinlets  carryinti'  silver  mim^rals  pass  out  from  the  vein  proper  and 
form  a  netwoi-k  in  the  adjacent  .schi.st  so  that  it  mav  locallv  serve  as  ore. 


PLATE   24. 


A.  MTARGYRITE  (M)  FILLING  CAVITIES  IN  EARLIER  QUARTZ 
(Q).  The  boundaries  are  controlled  by  the  crystalline  outline  of 
the  quartz.    30   dia. 


B.  BANDING  OF  PTRITE  (white)  AND  FINELY  CRYSTALLINE 
QUARTZ  (dark  gray).  The  banding  parallels  the  walls  of  the 
vein.      A  few  metasomes  of  niiargyrite    (M)    are  present:.       25  dia. 


37841— facing  p.  100. 


PLATE   25. 


A.  SILVER  ORE,  SHOWING  GENERAL  RELATIONS  OF  THE 
MINERALS.  Q  =  quartz  ;  A  =r  arsenopyrite  ;  Cp  =  chalcopyrite  ; 
M  =:  miargyrite  ;    P  ^  proustite.    140    dia. 


B.     MIARGYRITE    (M)    SURROUNDING    AND   REPLACING    STYLO- 
TYPITE   (P).      Q  =  quartz.    30  dia. 


37841 — facing   p.    101 


—  101  — 

In  the  silver  veins,  as  in  the  g:old  ami  tunirsten-heariiifi:  veins  of  the 
district,  the  first  material  to  be  deposited  consisted  of  very  fine-grained 
siliceous  material.  Suceeedinji'  o;(>nerations  of  silica  Ix'canic  irradiiallN' 
coarser  and  coaixM-  in  urain  until  the  hitest  to  be  deposited  is  found  as 
well-crystallized  quartz  lininii'  the  open  druses  and  cavities.  The  fine- 
m-ained  initial  phase  can  probably  jiere  again  he  ascribed  to  ra])id 
de[iosition  resulting  fi'oin  solutions  supersatni'ated  due  to  the  clianged 
conditions  of  temperature  and  pi-essnre  encountered  as  tlicv  approached 
the  surface.  The  coarser-grained  later  phases  resulted  from  the  slower 
deposition  from  the  solutions  which  \\-ere  becoiiiiiig  impoverished  in 
silica. 

Accompanying  the  early  phases  of  the  siliceous  nuiterial  some  j)yrite 
was  deposited  for  we  find  the  pyrite  in  extremely  fine  crystals  or 
crystalline  aggregates  intergrown  with  this  fine-grained  cpiartz  and 
chalcedony.  The  pyrite  was  de|)osited  both  intergrown  with  the  vein 
matter  and  replacing  the  wall  rocks  and  included  fi'agmeuts  of  schist. 

Tile  deposition  of  pyrite  was  interrupted  by  an  infiux  of  arsenic  in 
the  solutions  which  resulted  in  the  formation  of  arsenopyrite  instead 
of  the  pyrite  which  had  previously  formed.  Tlu^  pyrite  of  the  early 
stage  is  characteristically  found  in  aggregates  sui'rounded  l)y  an  aureol 
of  ar.senopyrite  crystals.  The  arsenopyrite  occurs  either  as  miinite 
crystals  or  crystalline  aggregates  intergrown  with  the  fine-grained 
siliceous  material. 

While  some  snmll  traces  of  silvei'  minerals  oi-cui-  intergrown  with  the 
earlier  minerals  to  form,  they  did  not  l)egin  to  form  in  important  fpianti- 
ties  until  after  most  of  the  arsenopyrite  had  been  deposited,  and  fairly 
coarse  (puirtz  was  being  deposited.  Pyrite  and  arsenopyrit(>  are  rarely 
found  included  in  the  silver  minerals.  The  silver  mitU'rals  character- 
istically occur  in  masses  whose  outline  as  seen  under  the  miscroscope  has 
been  controlled  by  pre-existing  quartz  crystals.  (See  Plate  2-1-A.) 

The  first  of  the  silver  minerals  to  form  in  impoi'tant  amounts  was 
st\iot\pite.  It  characteristically-  occurs  as  iri'egular  rounded  nuisses 
included  in  the  nii;iri^yrite.  Associated  with  the  stylotypite.  and 
apparently  contemporaneous  with  it  are  small  (|iiaii1  ities  of  chalcopyi-ite 
and  argentiferous  b(7rnite    (?). 

In  the  polished  surface,  as  observed  under  the  microscope  using 
vertical  illumination,  the  stylotypite  is  abnost  invariably  found  to  be 
highly  pitted  due  to  the  inclusion  of  innumerable  minute  inclusions  of 
quartz.  Apparently  the  i)eriod  of  formation  of  the  stylotypite  was 
contemporaneous  with  that  of  the  minute  (luartz  crystals  which  were 
included  in  the  growing  stylotypite. 

These  minute  (|uartz  inclusions  are  never  found  in  the  miargyrite  and 
j)yrargyrite.  On  the  contrary  these  two  minerals,  which  occur  inter- 
grown together  (the  pyrargyrite  being  noticeal)ly  subordinate),  charac- 
teristically occur  filling  spaces  whose  shape  is  controlled  by  crystalline 
(piartz.  It  follows  that  the  formation  of  the  miargyrite  and  pyrargyrite 
postdates  that  of  the  quartz. 

The  miargyrite  also  was  observed  to  occasionally  fill  fractures  cut- 
ting the  stylotypite,  and  its  general  relations  to  that  mineral  are  such 
that  it  is  believed  that  the  miargyrite  in  i)art  replaces  the  stylotypite. 
The  presence  of  numerous  miargyrite  crystals  in  tlie  open  druses  and 
vugs  is  further  evidence  of  its  late  period  of  formation. 


—  102  — 

The  jKn-iod  of  formation  of  tlio  proustite  roughly  corresponds  to  the 
latter  i)art  of  the  period  of  formation  of  the  miarg\^rite,  for  we  find 
mieroscopic  intergrowths  of  the  two  minerals;  we  find  proustite  ocenr- 
r\ng  in  veinlets  cutting  the  miargyrite;  and  we  find  the  proustite  as 
crystals  occurring  in  open  druses  and  vugs.  All  of  the  minerals  so  far 
mentioned  are  found  to  be  occasionally  cut  by  fractures  filled  with 
white  quartz  or  with  pyrite.  Sometimes  the  pyrite  occurs  filling  open- 
ings left  in  the  centers  of  the  fractures  after  some  quartz  had  been 
deposited.  The  fractures  can  be  taken  as  evidence  of  movements  in 
progress'  during  the  period  of  mineralization.  The  occurrence  of  pyrite 
in  these  fractures  is  indicative  of  a  second  period  of  formation  of  the 
pyrite. 

The  calcite  was  one  of  the  latest  minerals  to  form,  occurring  in 
fractures  cutting  the  previoush'  deposited  ore,  or  else  in  open  drusy 
cavities.    The  calcite  commonly  contains  included  crystals  of  miargyrite. 

The  stibnite  also  was  formed  durinsr  the  latter  part  of  the  period  of 
mineralization,  since  it  has  oidy  l)een  observed  filling  fractures  cutting 
the  other  ore  minerals,  or  as  well-developed  crystals  formed  in  drusy 
cavities.  The  presence  of  stibnite  as  the  last  or  one  of  the  la.st  minerals 
to  form  is  suggestive  that  during  the  last  stages  of  the  mineralization 
the  solutions  were  becoming  impoverished  in  silver. 

But  little  opportunity  was  had  to  study  the  secondary  mineralization 
due  to  lack  of  material.  From  the  little  study  Avhich  was  made,  how- 
ever, certain  rather  general  conclusions  can  ])e  drawn. 

The  enrichment  has  been  confined  to  comparatively  shallow  depths, 
enriched  ores  being  found  only  in  the  upper-few  levels  of  the  California 
Rand  Silver  ]\[ine.  No  trace  of  secondary  silver  minerals  was  found  in 
specimens  obtained  as  high  as'  the  sixth  level. 

Enrichment  which  was  observed  occurs  chiefiy  through  the  direct 
replacement  of  the  primary  silver  minerals  by  cerargyrite.  (See  plate 
27-B).  To  a  lesser  extent  the  primary  silver  minerals  were  being 
replaced  by  secondary  sulphides,  probably  stephanite  in  part.  A 
further  enrichment  of  the  ore  resulted  from  the  destruction  and  removal 
of  the  pyrite  and  arsenopyrite  present  in  the  primary  ore. 

ALTERATION   OF  THE  WALL   ROCK. 

Where  schist  is  the  wall  rock,  the  chief  effects  of  alteration  which 
were  produced  by  the  mineralizing  solutions  were  those  of  silicification 
and  pyritization,  and  destruction  of  the  pre-existing  feldspars  and  fer- 
romagnesian  minerals.  The  silicification  which  has  occurred  has 
resulted  from  the  development  of  granular  quartz  which  is  strung  out 
in  the  direction  of  the  schistosity.  The  pyritization  shows  a  somewhat 
similar  relation  to  the  schistosity.  This  type  of  alteration  effects  both 
the  wall  rocks  proper  and  also  the  schist  fragments  included  in  the 
vein  matter. 

Where  diabase  is  the  Avail  rock  it  is  found  to  be  somewhat  similarly 
effected.  The  most  noticeal)le  change  is  the  complete  destruction  and 
removal  of  the  ferromagnesian  minerals,  with  a  resulting  whitening  and 
softening  of  the  rock.  The  resulting  product  is  a  soft  and  somewhat 
chalky  rock,  light-gray  to  white  in  color,  which  is  cut  by  numerous 
siliceous  veinlets  and  veinlets  of  pyrite.  P^'rite  also  occurs  shot  through 
tlie  mass  of  the  rock. 


pi.ATE  ■:<;, 


A.  GENERAL  RELATIONS  OF  MINERALS  OF  SILVER  ORE. 
Qmr  quartz;  A  r=arsenopyrite  ;  P  =  stylotypite  ;  M=:r  miargyrite  ; 
B=r  argentiferous  bornite(?).     220  dia. 


m 


'flff 


B.  GENERAL  RELATIONS' OF  SILVER  MINERALS.  Q  —  quartz  ; 
A  =  arsenopyrite  ;  M  r=  miargyrite  ;  P  =:  stylotypite  ;  B  =:  argentif- 
erous borniteC?).     220  dia. 


37841 — facing  p.    102 


I 


PLATE    27. 


A.  SILICIFICATION  OP  THE  SCHIST  WALL,  ROCKS  OP  THE 
SILVER  VEINS.  The  granular  aggregates  consist  of  quartz 
developed  at  the  time  of  the  mineralization.    50  dia.    X  nicols. 


B.  ALTERATION  OF  METALLIC  SILVER  MINERALS.  The  white 
mineral  is  probably  miargyrite  altering  to  cerargyrite  (light  gray). 
The  dark  gray  mineral  is  quartz.    25  dia. 


37841 — facing   p.    103 


103 


ORDER  OF   FORMATION   OF  THE   MINERALS. 

PRIMARY  SECONDARY 

Chalcedony Quartz 


Silica 

Pyrite 

Arsenopyrite 

Stylotypite 

Chaleopyrite 

Arg.  Boniitc 

IMiai'gyrite 

Pyrargyrite 

Proustite 

Stibnite 

Calcite 

Seeondarj-  Su 

Cerargyrite 

Melanterite 


—  104  — 

AGE  AND  GENESIS  OF  THE  DEPOSITS. 

'riic  silver  (l('])()sits  are  clearly  of  ri)])er  ^[ioceiie  age,  and  slightly 
younger  than  the  gold  oi'es  of  the  (|nadrangle. 

At  several  places,  most  notal)l\"  in  the  workings  of  the  Numher  6 
Shaft  of  the  California  Rand  Silver  Mine  and  in  the  Fox  Lease  work- 
ings, silver-bearing  veins  cut  diabase  dikes.  The  diabase  itself  is  miner- 
alized and  locally  carries  values  in  silver.  The  dialiase  dikes  are  known 
to  cut  the  lower  beds  of  the  Rosamond  series  which  is  of  Upper  INIiocene 
age.    Locally  the  Rosamond  series  is  itself  mineralized. 

On  the  lith  level  of  the  California  Rand  Silver  Mine,  the  Williams 
Vein,  a  vein  of  the  northeast-southwest  system  cuts  a  gold-bearing  vein 
similar  to  others  of  the  gold  veins  of  the  quadrangle,  which  strikes 
N.  60°  E.  and  dips  60°  SE.  Fragments  from  the  gold  vein  are 
cemented  in  the  Williams  Vein,  while  unfilled  portions  of  the  Williams 
Vein  pass  directly  across  the  projection  of  the  gold  vein.  Assays  from 
the  gold  vein  show  from  $5.00  to  $75.00  per  ton  in  gold  accomi)anied 
by  only  an  ounce  or  two  in  silver. 

The  upper  limit  of  age  is  slightly  nu)re  difficult  to  fix.  A  detrital 
fragment  of  silver  ore  is  reported  to  have  been  found  on  the  dump  of 
the  Big  4:  shaft,  when  the  shaft  was  approximately  900  feet  deep  in  the 
Rosamond  series.  The  writer  was  unable  to  secure  a  piece  of  the 
rei)orted  find  wliicli  showed  any  trace  of  its  detrital  origin. 

Perhaps  the  best  evidence  which  may  be  used  to  fix  the  upward  limit 
in  age  of  the  silver  mineralization  is  to  be  found  in  the  mineralization 
of  tile  Rosamond  beds  adjacent  to  the  rhyolitic  and  diabasic  intrusives 
which  cut  them.  Assays  as  high  as  700  oz.  in  silver  and  $15.00  gold 
per  ton  are  said  to  have  been  obtained  locally  from  such  occurrences. 
These  values  are  directly  related  to  the  location  of  the  intrusives  so  that 
it  seems'  certain  that  they  were  introduced  by  the  intrusives. 

It  follows,  therefore,  that  the  silver  deposits  were  formed  during  the 
early  ITpper  IMiocene  by  a.scending  hot  solutions  which  closely  followed 
these  intrusives.  The  solutions  were  probably  directly  related  to  the 
deep-seated  underlying  magmatic  reservoir  from  which  the  intrusives 
were  derived. 

The  structural  conditions  are  such  that  the  u|iper  portion  of  the 
deposits  being  worked  by. the  California  Rand  Silver  ]\Iine  must  have 
been  within  a  few  hundred  feet  of  the  .surface  at  the  time  the  veins 
were  being  formed.  It  would  follow  that  the  pressures  existent  were 
low. 

The  silver  deposits,  therefore,'  are  clearly  epithermal  in  type. 

Origin   of  the  Veins. 

The  earth  movements  which  formed  the  fractures  in  which  the 
northeast-southwest  system  of  veins  were  developed  appear  to  have 
been  largely  horizontal,  for  the  fiat  fault  which  caps  the  veins  is  cut  at 
the  most  by  only  slight  vertical  offsets.  Furthermore,  much  of  the 
slickensiding  along  the  walls  of  the  veins  is  horizontal,  though  locally 
it  may  have  almost  any  attitude. 

These  northeast-southwest  fractures  were  completely  filled  by  the 
hard,  dense,  fine-grained  siliceous  vein  matter  early  in  the  period  of 
the  silver  mineralization.  Later  mcn-ements  which  would  ordinarily 
hiwe  been  I'elieved  along  these  lun-fheast-southwest  fractures  found 
tlii-ni    rightly    cemented    and   stronger   than   the   other  adjacent   rocks. 


—  105  — 

Loyally  these  later  iiioveinents  hreeeiated  the  vein  matter  previously 
(h'pitsited.  hut  in  j^eueral  these  latei-  ni(tvenients  i-esnlled  in  tlie  (h'vehip- 
meut  of  a  uew  set  of  'torsion  fraetures'  striking-  roughly  uorth,  within 
the  zone  in  which  the  vein  matter  had  been  previously  deposited.  The 
north  strike  of  these  later  secondary  fractures  would  indicate  that  the 
southeast  side  of  the  vein  system  was  tending  to  move  northeast,  while 
tlie  northwest  side  was  tending  to  move  southwest. 

Continuation  of  the  mineralization  resulted  in  tlie  deposition  in  these 
later  north-south  fractures  and  in  those  i)ortions  of  the  northeas-t- 
southwest  veins  whieli  had  lieen  hi-eceiated  of  more  vein  matter  and 
abundant  silver  minerals. 

Comparison  of  the  general  tenoi-  of  the  ores  mined  from  the  north- 
ea.st-.southwest  veins  whieli  escaped  hrecciation  (i.  e.  the  Foot  wall  Vein), 
with  those  mined  in  the  north-south  veins  and  the  northeast-southwest 
veins  which  were  brecciated  iiulicates  that  the  earliest  of  the  mineraliz- 
ing solutions  were  verv-  rich  in  silica,  iron,  sulphur  and  arsenic,  while 
later  in  the  period  of  mineralization  the  solutions  became  impoverished 
in  silica,  iron,  and  arsenic  but  enriched  in  silver,  antimony  and  sulphur. 
This  variation  checks  the  results  obtained  from  the  microscopic  examiiui- 
tion  of  the  ores. 

STRUCTURAL  CONTROL  OF  THE  ORE  DEPOSITION. 

The  structure  of  tlu'  (lei)osits  which  has  alreadN'  be(>n  described  is 
such  that  solutions  ascending  the  fractures  in  which  the  veins  were 
later  deposited  were  stopped  or  at  least  hindered  in  their  further  ascent 
by  the  gouge  in  the  tiat  fault  which  cai)s  the  deposits.  It  is  a  matter  of 
observation  that  ore  deposition  commoidy  occurs  where  the  structural 
conditions  are  such  as  to  cause  stagnation  of  the  mineralizing  solutions. 

The  conclusion  would  innnediately  follow  that  since  the  structure 
which  existed  ])revious  to  the  deposition  of  the  orebodies  now  being 
worked  in  the  California  Rand  Silver  Mine  wa.s  such  as  to  cause  .stagna- 
tion of  the  ascending  solutions,  the  rich  orebodies  there  developed  are 
a  direct  result  of  structural  c()ntrol. 

Part  of  the  same  structure,  namely  the  flat  fault  with  its  impervi- 
ous goTige,  also  a))pears  to  have  been  responsible  for  the  coni|)aratively 
slight  amount  of  oxidation  and  secondary  enrichment  which  has 
occuri'ed.  It  is  probal)le  that  no  secondary  enrichment  exists  below  the 
4th  level  of  the  Califor-nia  Hand  Silver  Mine  (1!)4  feet  below  the  sur- 
face), while  above  this  level  primary  sulphides  ai'c  not  uncommon.  The 
4th  level  is  well  above  the  ground-water  level  which  if  not  pumped  Avoukl 
probably  stand  at  a  depth  of  from  500  to  600  feet  below  the  surface. 

It  seems  ])robable  that  l)ut  little  oxidation  or  enrichment  occurred 
|)revious  to  the  removal  of  the  tlat  fault  from  above  portions  of  the 
deposit  through  proccvSses  of  erosion,  most  of  the  alteration  now  present 
dating  from  that  tiiui-. 

POSSIBLE    EXTENSION    OF    THE    DEPOSITS. 

Two  conditions  apjiear  to  ha\e  Ijcen  necessary  for  the  formation  of 
^he  silver  deposits.  First  the  i)resence  of  the  ascending  mineralizing 
solutions,  and  second  the  presence  of  favorable  structure.  The  miner- 
alizing solutions  are  known   to  have  effected  a   wide  area.     To  what 


—  106  — 

extent  favorable  structural  conditions  existed  elsewhere  than  in  the 
property  of  the  California  Rand  Silver  Mine  yet  remains  to  be  seen. 

]\riK'li  of  the  area,  namely  that  to  the  south  and  west  of  the  California 
Rand  Silver  ]\Iine  luis  already  been  somewhat  thoroughly  prospected, 
traces  of  silver  mineralization  being  discovered,  l)ut  no  workable  depos- 
its having  as  yet  been  found. 

On  the  north  and  east  the  Fox  Lease  and  Silver  King  workings  have 
shown  that  the  veins  are  too  low  grade  to  work  or  else  do  not  continue 
through.  Only  a  comparatively  narrow  zone  remains  between  these 
two  properties  northeast  from  the  California  Rand  Number  6  Shaft 
for  possible  extension  of  the  veins  being  Avorked  in  the  California  Rand 
Silver  ]\Iine. 

Of  greater  interest  is  the  possibility  of  other  centers  of  mineraliza- 
tion having  occurred  as  the  result  of  favorable  local  structures.  The 
thick  cover  of  Rosamond  sediments  and  lavas  over  much  of  the  area 
which  possesses  potential  possibilities  greatly  hinders  the  work  of  pros- 
pecting as  Avell  as  adding  greatly  to  the  expense  involved. 

To  what  depth  ore  deposition  extended  is  as  yet  unanswered.  Tn  the 
California  Rand  Silver  Mine  the  orebodies  on  the  11th  level  are  just  as 
large  and  just  as  rich  as  they  were  on  the  higher  levels,  but  due  to  the 
merging  of  the  veins  in  depth,  the  amount  of  ore  available  in  a  given 
unit  of  ground  is  considerably  less.  If  the  remaining  veins  should  con- 
tinue to  merge  in  depth  without  increasing  in  size,  this  condition  Avill 
be  aggravated. 

The  ore  del^osition  is  known  to  have  occurred  under  conditions  of 
lempei'ature  and  pressure  existing  close  to  the  surface,  and  in  the 
known  deposits  the  ores  have  been  found  close  to  the  surface  except 
where  special  structural  conditions  have  existed.  It  must  be  concluded 
therefore  that  no  excuse  for  deep  exploration  exists  except  where  special 
sti-uctural  conditions  are  known  to  occur.  Such  special  conditions  are 
found  in  all  the  properties  lying  east  of  the  California  Rand  Silver 
Mine  under  the  cover  of  Rosamond  strata.  In  the  properties  to  the 
west,  however,  exploration  at  depths  greater  than  from  two  to  three 
hundred  feet  is  entirely  unjustified  for  the  possibilities  for  the  occur- 
rence of  orebodies  at  greater  depths  are  if  anything  less  than  are  the 
possibilities  for  their  occurrence  close  to  the  surface. 


CONCLUSION. 

The  three  stages  of  mineralization  which  have  been  recognized  all 
occurred  during  a  comparatively  short  period  in  early  Upper  Miocene 
time.  Mineralization  of  the  epithermal  type  is  notably  erratic.  The 
mineralizing  solutions  change  radically  in  composition  from  time  to 
time.  The  three  stages  of  mineralization  present  in  the  Randsburg 
(piadrangle  are  believed  to  be  stages  in  a  single  epoch  of  mineralization, 
during  Avhich  the  solutions  asceluling  from  the  same  deep-seated  mag- 
matic  reservoir  from  which  the  rhyolitic  and  diabasic  intrusives  were 
derived,  were  subject  to  radical  change  in  composition  so  that  initially 
they  deposited  tungsten  minerals ;  later  changing  to  gold ;  and  lastly 
to  silver. 

Pi'eceding  and  during  this  same  epoch  of  mineralization  which  accom- 
panied and  immediately  followed  the  shallow  igneous  intrusions,  earth 
movements,  apparently  compressional  in  nature,  were  active,  providing 


—  107  — 


a  means  of  ascent  for  the  solutions  as  well  as  structural  conditions 
favoi-able  for  the  (lei)osition  of  the  ores.  These  same  movements  pi-o- 
vided  channels  for  the  injection  of  the  earlier  igneous  intrusions. 

The  writer  can  not  resist  adding  the  conjecture  that  the  eartii  move- 
ments were  themselves  a  direct  result  of  the  weakening  of  the  earth's 
crust  due  to  the  presence  of  a  large  underlying  molten  ])lutonic  mass 
[during  the  early  Upper  ^Miocene,  from  whieh  it  would  follow  that  all 
the'  ])hases  of  the  ore  deposition  were  directly  dependent  on  subjacent 
igneous  activity. 


—  108  — 
PART  III.     HISTORY  OF  MINING. 


Some  pro.spectinti'  was  carried  on  witliiii  the  (|ua(lrangle  as  early 
as  the  'sixties,  but  it  was  not  until  18I>.'5  that  any  mineral  production 
was  made.  During  the  winter  of  tluit  year,  placer  gold  was  discovered 
at  Goler.  some  two  miles  west  of  the  edge  of  the  (puidrangle  near  the 
present  line  of  the  Southern  Pacific  Railroad.  Dry -washing  camps 
were  shortly  established  at  Goler,  Red  Rock  Canyon,  Last  Chance  Gulch 
and  Summit  Diggings.  Only  one  of  these  camps,  the  last  named,  lies 
within  the  Randsburg  quadrangle. 

The  Yellow  Aster  ^line,  originally  known  as  the  Olympus  Mine,  was 
located  in  April,  1895,  by  John  Singleton,  Fred  Mooers  and  C.  A, 
Burcham.  Other  discoveries  soon  followed  and  hundreds  of  claims 
were  staked.  The  town  of  Randsburg  grew  at  the  center  of  the  new 
gold  district. 

The  rich  ore  from  the  Yellow  Aster  Mine  was  at  first  shipped,  but 
within  a  short  time  the  proceeds  from  the  mine  were  sufficient  to  allow 
of  tile  erection  of  a  80-stamp  mill  which  began  operations  early  in  1901. 
A  100-stamp  mill  was  completed  the  same  year.  The  30-stamp  mill 
ceased  operations  in  1913,  but  the  other  continued  to  operate  until 
temporarily  closed  down  in  1918.  Since  then  a  few  stamps  have  o])er- 
ated  occasionally  on  leasers'  ore. 

In  1897  the  Santa  Fe  Railroad  constructed  a  branch  line  from 
Kramer  to  within  two  miles  of  Randsburg,  where  Johannesburg  is  noAv 
located. 

During  the  early  days  of  gold  mining,  the  miners  had  trouble  with 
a  heavy  white  mineral  which  interfered  with  the  concentration  of  the 
gold.  This  heavy  white  mineral  was  termed  'heavy  spar'  by  the 
miners  and  its  true  nature  was  not  recognized  until  1!)()3  when  it  was 
identified  as  scheelite.  Location  of  tungsten  claims  followed.  Scheelite 
at  that  time  was  worth  about  $3.00  per  unit.  A  consolidation  which 
later  developed  into  the  Atolia  Mhiing  Companv  was  started  earlv  in 
1906. 

Tli(>  price  of  scheelite  gradually  increased  until  it  reached  $7.00  per 
unit  in  1913.  In  191."),  as  a  result  of  the  demand  created  by  the  war,  the 
value  of  scheelite  increased  by  leaps  and  bounds.  In  1916  scheelite  was 
selling  for  as  much  as  $80.00  per  unit  in  the  oi)en  market. 

During  this  period  of  high  prices  the  ground  to  the  south  and  east 
of  Atolia,  locally  termed  the  'spud  patch,'  was  intensely  worked  for 
placer  scheelite  derived  from  the  weathering  of  the  veins  to  the  noi'th. 
Tungsten  placers  were  also  worked  further  north  in  Baltic  Gulch,  the 
scheelite  being  derived  from  the  gold  veins  of  the  Stringer  District. 

At  the  close  of  the  war  the  price'  of  scheelite  dropped  to  such  an 
extent  that  operations  decreased  all  the  i)roperties  l)eing  shut  down  by 
March  1,  1919.  They  remained  idle  until  the  spring  of  1924  when  the 
scheelite  market  advanced  to  the  point  that  leasing  operations  were 
resumed.  During  the  period  of  enforced  idleness,  Atolia  was  practi- 
cally deserted. 

On  April  12,  1919,  the  discovery  of  the  orebodies  now  being  worked 
by  the  California  Rand  Silver  Mine  was  made  by  Jack  Nosser  and 
W.  11.  Williams.     The  orighial  outcrop  of  the  ore  occurred  only  about 


—  109  — 

30  feet  from  a  well-traveled  road  on  the  Jiianita  Claim,  a  grold  property. 
Tlic  outcrop  contained  abundant  corar.tryrite.  assays  of  surface  material, 
sliowiu^^  some  -Wi)  ozs.  of  silver  and  )}  ozs.  of  {iold  per  ton.  The  Cali- 
fornia Rand  Silver  Mininji;  Company  was  soon  formed.  Mnch  of  the 
early  woi'k  on  the  holdiups  of  this  company  was  done  by  leasers. 

Dui'inf::  its  early  life,  the  California  Hand  Silver  Mine  was  literally 
without  a  dump.  The  initial  work  consisted  of  an  opening  in  the' 
sliaft  \'cin  which  was  17  feet  wide,  22  feet  long  and  75  feet  deep, 
commencing  at  the  surface.  All  of  the  rock  which  came  ont  of  this 
hole  was  hiiih  urade  ore  which  was  shipped  dii'ect  to  the  smelter,  pro- 
ducing over  $300,000. 
b  Ore  was  struck  on  only  one  of  the  leases,  that  operated  by  Mr. 
E.  T.  Grady.  This  lease  which  was  only  120  feet  square  and  450  feet 
deep  is  credited  with  a  protluction  of  1,487.742  oz.  of  silver  and  5480  oz. 
of  gold  from  the  18,222  tons  of  ore  which  were  mined  during  the  life 
of  the  lease. 

The  silver  deposit  was  at  first  Lieuei-ally  accepted  as  a  freak  which 
would  not  iiersist  with  depth.  But  as  its  true  nature  became  known, 
the  surrounding  ground  Avas  subjected  to  intense  exploration,  some 
forty  to  fifty  shafts  being  sunk  within  a  radius  of  less  than  a  mile. 
These  shafts  vary  from  fifty  to  1100  feet  in  depth,  probably  averaging 
al)out  ;]50  feet.  Prospecting  apparently  reached  its  peak  in  the  feverish 
activity  which  pervaded  the  region  during  1922  and  1923. 

During  the  life  of  the  Pittman  Act  with  its  guarantee  of  $1.00  per 
ounce  foi-  domestic  silver,  the  operators  of  the  California  Rand  Silver 
.Mine  made  every  possible  effort  to  produce  as  much  silver  as  possible. 
It  was  during  this  period,  that  much  of  the  high-grade  ores  of  the 
deposit  were  exploited. 

The  expiration  of  the  Pittman  Act  in  1923,  with  the  resulting 
decrease  in  the  value  of  the  silver  produced,  apparently  made  but 
little  difference  in  the  operations  of  the  California  Rand  Silver  Mine, 
though  it  must  have  noticeably  increased  the  lower  limit  of  value  of 
ore  which  could  be  profitably  mined.  The  decrease  in  the  price  of  silver, 
however,  hatl  a  deterrent  effect  0)i  the  exploration  of  surrounding 
properties. 

The  California  Rand  Silver  ^Mining  Company  started  the  erection 
of  a  100-ton  flotation  mill  in  Se])tember,  1921,  and  on  December  15 
of  the  same  year  it  commenced  operations.  Later,  the  capacity  of  the 
mill  was  increased  to  400  tons  per  day. 

The  latest  reports  from  the  camp  indicate  that  the  California  Rand 
Silver  properties  have  been  unable  to  keep  the  development  of  ore 
sufficiently  ahead  of  the  production  to  keep  the  mill  running  at  full 
capacity,  so  that  commencing  early  in  the  spring  of  1924  the  mill 
was  being  operated  during  onlv  one  shift  each  dav. 


—  110  — 

PART  IV.    MINES  AND  PROSPECTS. 


Ill  the  following  brief  description  of  the  mines  and  prospects  of  the 
Randsburii'  (|ua(lran^le,  no  attempt  at  completeness  has  been  made,  the 
data  here  presented  being  considered  to  be  entirely  subordinate  to  the 
main  purpose  of  the  report. 

The  majority  of  the  properties  here  described  -were  examined  by  the 
writer  personally,  though  in  many  cases  much  of  the  description  must 
be  classed  as  'second  hand'  being  the  result  of  interviews  with  those 
ill  charge  of  the  operation  of  the  properties. 

Many  of  the  older  mines  of  the  quadrangle  are  not  now  operating, 
the  workings  in  many  cases  being  inaccessible.  For  the  most  part,  no 
miMition  will  be  made  of  such  properties. 

The  three  large  producers  of  the  district  are  treated  first,  followed 
alphabetically  by  the  remaining  mines  and  prospects.  Some  mention 
at  least  is  made  of  all  of  the  properties  which  were  operating  at  the 
time!  of  the  writer's  visits,  with  one  exception  of  a  property  which 
the  writer  was  refused  permission  to  examine. 

CALIFORNIA  RAND  SILVER  MINE. 

This  property  is  operated  by  the  California  Rand  Silver,  Inc.,  whose 
head  office  is  in  Bakersfield.  This  company  holds  eleven  claims  or 
fractions  surrounding  the  California  Rand  Silver  Mine,  as  well  as  nine 
claims  which  are  under  lease  to  the  St.  Lawrence  Rand  Mining 
Company. 

The  California  Rand  Silver  Mine  is  developed  by  approximately 
seven  miles  of  drifts  and  crosscuts,  and  by  a  number  of  shafts,  all  of 
which  have  practically  been  abandoned  except  the  No.  1,  the  No.  2, 
and  the  No.  6. 

The  No.  1  shaft  (2-compartment)  is  inclined  at  an  angle  of  seventy- 
three  degrees  to  the  horizontal,  roughly  following  the  dip  of  the  Shaft 
Vein.  It  extends  down  to  the  11th  level,  a  vertical  depth  of  660  feet 
below  the  collar  of  the  shaft.  Throughout  its  length  it  is  in  schist  or 
vein  matter.     It  is  dry  at  the  bottom. 

The  No.  2  shaft  (2-compartment)  is  vertical,  extending  to  a  depth  of 
1003  feet.  The  shaft,  excepting  a  small  thickness  of  overburden  near 
the  surface,  is  entirely  in  schist.  Water  was  struck  at  a  depth  of  715 
feet,  5000  gallons  per  day  being  produced.  The  14th  level  is  at  present 
the  lowest  level  connecting  with  the  No.  2  shaft. 

The  No.  6  shaft  (single  compartment)  on  the  northern  part  of  the 
property  is  also  vertical.  It  is  785  feet  in  depth  and  has  a  little  water 
at  the  bottom.  It  entered  the  schist  at  a  depth  of  560  feet  below  the 
collar,  the  material  above  that  point  consisting  chiefly  of  Rosamond 
sandstones  with  a  small  thickness  of  overburden  near  the  surface. 
Levels  are  cut  at  depths  of  610,  660  and  720  feet.  As  yet  none  of  the 
Avorkings  have  connected  with  the  workings  of  the  main  mine  to  the 
south. 

In  the'  main  mine  the  levels  are  somewhat  irregularly^  spaced  down  to 
the  11th  level,  the  level  interval  being  about  60  feet.  Between  the  11th 
and  14th  levels,  the  level  interval  is  100  feet,  although  as  yet  only  the 
stations  have  been  cut  on  the  12'th  and  13th  levels. 


—  Ill  — 

Duo  to  tlie  complicated  iiaturi'  of  the  veins  on  the  upper  h'vels,  it 
was  found  necessary  in  the  mining  operations  to  'follow  the  ore.' 
Tliis  resulted  in  many  parallel  drifts  and  closely-spaced  crosscuts.  On 
the  lower  levels,  due  to  the  mergence  of  many  of  the  veins,  the  drifts 

PI.ATK   2!». 


ISL 


^*k  «•—;,« 


rrrrrHjji 


A.    IIEADFRAME   OF  NO.   2    SHAFT   ANlJ  MILL  OF  THE  CALIFORNIA   RAND 

SILVER    MINE. 


B.    NEW    SHAFl^    (left)     AND    OLD    SHAFT     (right)     OF    THE    UNION    MINE 

NEAR    ATOLIA. 

have   been   run  much   farther   apart,    with   consequently   longer   and 
fewer  crosscuts. 

The  veins,  of  which  two  systems  can  be  recognized,  occur  cutting  the 
Eand  schist,  which  as  exposed  in  the  mine  is  ordinarily  slightly  rolling, 


—  112  — 

usually  clipping;  at  low  ang-les  to  the  east  or  southeast,  though  occasion- 
ally  reverse   dips  occur. 

The  schists  exposed  in  the  mine  are  quite  similar  in  all  respects  to 
the  other  schists  of  the  Rand  series  exposed  elsewhere.  Both  mica- 
albite  schists  and  amphibole  schists  have  been  recognized  in  the  mine. 
Adjacent  to  the  veins,  these  schists  are  commonly  rather  hig'hly  altered 
and  frequently  silicified  and  cut  by  siliceous  veinlets  and  pyrite.  The 
walls  of  the  veins  are  quite  commonly  more  or  less  indefinite  and 
gradational. 

Ca])ping'  the  veins  is  a  pre-mineral  fault  possessing  a  low  easterly 
dip.  This  fault  and  its  control  of  the  mineralization  has  already  been 
described. 

NORTHEAST  VEINS. 

Footwall  Vein. 

The  only  veins  which  possessed  outcrops  are  the  Footwall  Vein  and 
a  small  segment  of  the  Shaft  Vein.  The  Footwall  Vein,  while  carrying 
some  silver  throughout,  is  of  too  low  grade  to  be  exploited.  Besides 
its  known  surface  outcrop,  it  has  been  crosscut  on  the  1st  level  just 
north  of  the  No.  1  shaft  where  30  feet  of  very  dense  vein  matter  is 
exposed ;  on  the  2nd  level  northwest  from  the  Blanck  Shaft  where'  over 
60  feet  of  little-fractured  vein  matter  is  exposed ;  and  again  on  the  3rd 
level  to  the  north  of  the  No.  1  shaft. 

Shaft  Vein. 

The  original  discovery  was  made  on  the  Shaft  Vein  at  the  only  point 
where  it  outcropped.  The  surface  material  assayed  over  300  oz.  of 
silver  and  3  ozs.  of  gold  per  ton.  The  Shaft  Vein  has  been  stoped 
between  the  1st  level  and  the  surface  from  a  point  60  feet  noith  of  the 
shaft  to  a  point  105  feet  south  of  the  shaft,  aiul  between  the  2iul  and 
1st  levels  for  a  distance  of  40  feet  to  the  south  of  the  shaft.  The  vein 
through  this  distance  varies  from  10  to  20  feet  in  thickness.  All  of 
the  ore  was  oxidized  and  iron  stained,  the  silver  occurring  chiefly  as 
ce'rargyrite.  The  total  ore  removed  averaged  $120.57  per  ton,  chiefly 
in  silver.  Below  the  2nd  level  the  value  dropped  to  2|  to  4  oz.  of  silver 
per  ton. 

The  Shaft  Vein  has  recently  been  intersected  on  the  14th  level  where 
the  only  trace  of  valuable  mineralization  so  far  encountered  in  it  has 
been  a  small  quantity  of  free  gold  and  miargyrite  ( ?)  found  in  a 
fracture. 

The  Shaft  Vein  has  probably  not  long  been  exposed  from  beneath 
the  fiat  fault  (the  'mud  wall'),  for  this  fault  may  be  observed  top- 
ping the  drift  of  the  first  level  only  a  hundred  feet  north  of  the  shaft. 

Antimony   Vein. 

The  Antimony  Vein  is  the  third  vein  from  west  to  east  which 
belongs  to  the  northeast  vein  system.  It  is  one  of  the  larger  and  more 
continuous  veins  of  the  mine,  probably  averaghig  between  ten  and 
fifteen  feet  in  thickness.  It  ordiiuirily  is  composed  of  a  dense  gray 
siliceous  vein  matter  which  is  commonly  banded.  In  part,  however,  it 
has  been  brecciated  by  movements  which  were  later  than  the  deposition 
of  most  of  the  vein  matter,  but  which  were  probably  contemporaneous 
or   earlier  than   the   more   important  phase   of   silver   mineralization. 


—  113  — 

Tt  appears  probable  that  the  vein  owes  much  of  its  silver  content  to  this 
hreeeiatioii  which  opened  a  passajie  for  the  later  mineralizing  solutions. 

Only  a  comparatively  small  amount  of  ore  has  beeli  mined  from  the 
Antitnony  Vein,  the  vein  havinji'  been  stoped  throutrh  a  distance  of 
approximately  40  feet  between  the  3rd  and  4tli  levels,  the  ore  averaging 
about  $14.00  per  ton ;  and  for  55  feet  between  the  5th  and  6th  levels,  the 
ore  varying  from  $9.50  to  $204  per  ton.  The  vein  carries  good  values 
on  both  the  7th  and  9th  levels. 

The  Antimony  Vein  is  terminated  upward  by  the  fiat  fault  between 
the  2nd  and  3rd  levels.  It  apparently  parses  into  the  fault  gouge  for 
a  short  distance  in  places  before  tinally  being  terminated.  The  vein  is 
well  exposed  on  the  10th  and  11th  levels,  but  apparently  carries  only  a 
low  silver  content  below  the  9th  level  where  it  is  intersected  by  an 
unnamed  flat  vein.     (See  later.) 

Alpha   Vein 

The  Alpha  Vein  also  belongs  to  the  northeast  vein  system,  being  a 
westward-dipping  spur  of  the  Antimony  Vein,  splitting  away  from  that 
vein  between  the  6th  and  7tli  levels.  The  Alpha  Vein  is  also  termi- 
nated upward  by  the  flat  fault,  in  places  above  the  3rd  level,  but  in 
general  just  below  that  level. 

Cei'tain  portions  of  the  Alpha  Vein  have  carried  good  values.  Above 
the  4th  level,  ore  extracted  from  a  length  of  140  feet,  varied  in  value 
from  $30  to  $60  per  ton.  Between  the  4th  and  5th  levels  the  values 
were  from  $9  to  $89  through  a  length  of  280  feet,  while  between  the 
5th  and  6th  levels  the  values  ranged  from  $10  to  $153  through  a  dis- 
tance of  180  feet. 

Williams  Vein. 

The  only  remaining  vein  of  the  northeast  system  so  far  known  in 
the  California  Rand  Silver  Mine  is  the  Williams  Vein,  lying  near  the 
pastern  edge  of  tlie  property.  The  AVilliams  Vein  possesses  a  mean 
trike  of  N.  40°  E.  and  is  nearly  vertical,  dipping  at  an  angle  of  about 
^0  degrees  to  the  southeast.  It  is  best  known  between  the  8th  and  11th 
levels,  though  probably  being  exposed  in  the  extreme  south  drift  ot 
the  7th  level.  This  vein  vai'ies  in  thickness  from  about  3  to  12  feet, 
le  walls  being  gi-adational  and  indefinite  as  are  the  walls  of  most  of 
^he  veins.  The  wall  rock  of  this,  as  of  most  of  the  veins  of  the  mine, 
ire  commonly  more  or  less  silicified  and  cut  by  fine  veinlets  of  quartz 
for  varying  distances  from  the  vein,  though  locally  such  silicification 
lay  be  entirely  absent.  The  Williams  Vein  is  quite  characteristically 
frecciated,  and  shows  other  evidence  of  inter-  and  post-mineral  move- 
lents.  The  metallic  silver  minerals  quite  commonly  occur  in  openings 
the  vein,  the  openings  being  due  to  both  brecciation  and  to  lack  of 
Complete  filling  of  the  vein. 

Much  of  the  ore  which  has  been  extracted  from  the  Williams  Vein 
las  been  of  good  grade.  On  the  10th  level,  the  ore  varied  from  $14.00 
\o  $28.00  through' a  distance  of  200  feet  along  the  vein,  while  on  the 
Llth  level,  through  a  length  of  240  feet  the  ore  ranged  from  $10.00  to 
^180.00  per  ton.  During  the  time  of  the  writer's  first  visit  to  the 
)roperty,  57  tons  of  ore  were  removed  from  a  stope  above  the  llth 
ivel  which  gave  averag'e  returns  of  $619.27  per  ton. 

S — 37841 


—  11'4  — 

On  the  11th  level  the  Williams  Vein  is  seen  to  cut  through  a  'gold 
vein.'  The  latter  vein  strikes  N.  60°  E.  and  dips  60°  SE.  Near  the 
point  of  intersection  the  'gold  vein,'  which  is  composed  of  white 
quartz  of  fine  grain,  quite  different  in  appearance  from  the  gangue  of 
the  silver  veins,  carries  from  $20.00  to  $75.00  per  ton  in  gold,  accom- 
panied by  only  an  ounce  or  two  of  silver.  The  gold  ore  near  the  point 
of  intersection  is  found  to  be  badly  brecciated,  the  quartz  fragments 
being  set  in  a  gray  siliceous  and  pyritic  matrix  similar  to  the  gangue 
of  the  silver  veins.  In  addition,  the  structure  of  the  Williams  Vein 
(banding,  etc.)  can  be  traced  directly  through  the  gold  vein.  The 
Williams  Vein  is  certainly  the  younger  of  the  two  veins. 

The  north  heading  of  the  drift  following  the  Williams  Vein  shows 
badly  altered  diabase  occurring  as  a  wall  to  the  vein  instead  of  the 
normal  schist  of  the  Rand  series  which  ordinarily  forms  the  vein  walls. 
The  diabase  is  largely  altered  to  a  compact  white  soapy  rock,  shot  full 
of  pyrite  and  cut  by  siliceous  veinlets,  so  that  it  is  only  in  local  frag- 
ments that  its  nature  can  be  recognized. 

NORTH-SOUTH   VEINS. 
Blanck  Vein. 

The  Blanck  Vein  strikes  N.  10°  E.,  and  dips  steeply  to  the  east.  It 
has  a  maximum  length  of  approximately  2'00  feet,  lying  diagonally 
between  the  Shaft  Vein  and  the  Antimony  Vein.  The  intersection 
with  the  Shaft  Vein  occurs  near  the  No.  1  shaft.  The  Blanck  Vein  has 
been  explored  on  the  4th  and  all  higher  levels  but  has  produced  com- 
paratively little  ore.  Much  of  the  vein  matter  carries  only  a  few  ounces 
of  silver  per  ton,  though  some  ore  carrying  approximately  4.")  ozs.  of 
silver  per  ton  has  been  mined  from  it.    Most  of  the  vein  is  oxidized. 

Frog  Vein. 

The  Frog  Vein,  just  north  of  the  Blanck  Vein,  lies  diagonally  between 
the  Alpha  Vein  and  the  Shaft  Vein,  apparently  cutting  across  the  Anti- 
mony Vein.  It  merges  with  the  Blanck  Vein  in  depth,  due  to  its  possess- 
ing a  north  strike  and  a  slightly  steeper  dip  than  the  Blanck  Vein. 

The  Frog  Vein  has  been  stoped  through  varying  lengths  from  near 
the  surface  to  the  3rd  level,  below  which  it  merges  with  the  Blanck 
Vein.  The  ore  near  the  surface  was  worth  al)out  $128  per  ton.  The 
vein  was  stoped  through  a  distance  of  160  feet  on  the  1st  level,  160 
feet  on  the  2nd  level,  and  40  feet  on  the  3rd  level.  The  ore  stoped 
varied  in  value  from  $22  to  $423  per  ton.  Practically  all  of  the  ore 
removed  was  oxidized. 

Treasure   Box  Vein. 

The  Treasure  Box  Vein  strikes  north  and  dips  steeply  to  the  east. 
It  lies  just  north  of  the  Frog  Vein,  forming  a  segment  between  the 
antimony  and  Shaft  veins,  and  possessing  a  maximum  length  of  about 
160  feet.  Like  the  Frog  Vein,  it  merges  with  the  Blanck  Vein  near 
the  3rd  level.  The  chief  stoping  in  this  vein  was  done  between  the 
1st  and  2nd  levels,  the  ore  removed  possessing  a  silver  content  of  from 
$34  to  $135  through  a  length  of  100  feet  along  the  vein.  The  ore  was 
oxidized.  Above  the  1st  level  the  Treasure  Box  Vein  is  terminated 
upward  through  most  of  its  length  b}-  the  flat  fault. 


—  115  — 

One  of  the  richest  pieces  of  ore  found  in  the  mine  came  from  the 
Treasure  Box  Vein  on  the  3r(l  level.  It  coiisisted  larorely  of  cerar^ryrite, 
secondary  sulphides,  probably  stephanite  in  part,  and  traces  of  primary 
miaruyi'ite.  Assay  returns  indicated  13,000  ounces  of  silver  per  ton. 
The  photo^aph  from  which  Plate  27-B  was  made  was  taken  from  this 
specimen. 

Rourke    Vein. 

Tbe  Ennrke  Vein  forms  a  shoi-t  seuiiieut.  approximntiuq:  l^^^O  feet  in 
maximum  length,  l.viiin'  between  the  Alpha  and  Antimony  veins,  and 
.just  west  of  the  Frog  Vein.  It  strikes  N.  10°  E.,  dipping  steeply  to 
the  east.  It  is  terminated  downward  by  the  Frog  Vein  with  which  it 
merges,  and  upward  near  the  2nd  level  by  the  flat  fault.  It  has  been 
stoped  for  a  length  of  about  20  feet  betweeen  the  2nd  and  8rd  levels,  the 
ore  removed  possessing  a  value  of  $16.50  per  ton. 

L  Jameson   Vein. 

The  Jameson  Vein  lies  to  the  east  of  the  Frog  Vein,  being  terminated 
on  the  south  by  the  Alpha  Vein,  while  to  the  north  it  appears  to  pass 
thi'ough  the  Antimony  \^'in  aiul  merge  with  the  Treasure  Box  Vein. 
The  vein  possesses  a  maximum  length  of  approximately  120  feet,  strik- 
ing a  little  west  of  north  and  standing  nearly  vertical.  It  is  terminated 
downward  by  the  Alpha  and  Treasure  Box  Veins,  and  upward,  near 
the  211(1  level  by  the  flat  fault.  The  Jameson  Vein  has  been  stoped 
l)etween  the  2nd  and  4th  levels  through  distances  of  from  50  to  80 
feet,  the  ore  removed  ranging  in  value  from  $40  to  $266  per  ton. 

No.  3  Stope. 

A  zone  eharacteri/ed  by  numerous  intersecting  stringers  and  veinlets, 
so  highly  mineralized  as  to  constitute  good  ore,  was  found  in  that 
portion  of  the  mine  bounded  by  the  Alpha  Vein  on  the  south  and 
l)ott()m,  the  Jameson  Vein  on  the  east,  the  Antimony  Vein  on  the 
north  and  west  and  the  Frog  Vein  on  the  west.  This  zone  was  stoped 
from  the  4tli  level  upward  for  65  feet  to  the  fiat  fault.  The  mass 
stoped  is  of  somewhat  irregular  shape,  having  a  maximum  diameter  of 
al)out  50  feet. 

The  schist  composing  the  nuiss  as  a  whole  had  been  highly  shattered 
and  fractured  and  more  or  less  silicified.  The  fractures,  which  had 
a  general  trend  of  north  and  south,  were  largely  filled  with  miargyrite 
and  other  jirimary  silver  minerals.  ]\fany  of  these  veinlets  of  miargy- 
rite were  an  inch  in  thickness.  Some  5000  tons  of  ore  were  removed 
from  the  No.  3  Stope,  the  average  value  being  $40  per  ton.  The  range 
in  value  as  mined  was  from  $33  to  $115  per  ton. 

518  and  530  Veins. 

Branching  from  the  west  side  of  the  Alpha  Vein,  about  250  feet  east 
of  the  No.  1  shaft,  are  several  small  irregular  veins.  The  518  Vein, 
where  it  branches  from  the  Alpha  Vein,  strikes  slightly  east  of  north 
but  gradually  swings  to  the  northeast,  again  merging  with  the  Alpha 
Vein  220  feet  from  where  it  branched.  Two  short  segments,  each  about 
80  feet  in  maximum  length  cut  from  the  Alpha  Vein  to  the  518  Vein 
within  this  distance. 


I 


—  116  — 

This  group  of  veins  is  terminated  downward  by  the  Alpha  Vein  near 
the  5th  level,  and  upward  by  the  Hat  fault  above  the  4th  level.  The 
518  Vein  has  been  stoped  through  a  length  of  approximately^  100  feet, 
the  ore  varying  in  value  from  $26  to  $726  per  ton. 

Sill  Vein. 

The  Sill  Vein  is  one  of  the  more  important  of  the  north-south  veins 
of  the  property,  having  been  worked  from  the  7th  to  the  9th  level. 
The  vein  strikes  about  N.  20°  W.,  dipping  rather  steeply  to  the  east. 
It  is  terminated  upward  by  the  Alpha  Vein  and  the  fiat  fault.  On 
tlie  north  it  ends  against  the  Antimony  Vein.  Near  the  9th  level  it 
merges  with  or  is  cut  off  by  a  flat  and  as  yet  unnamed  vein.  Its 
southern  termination  is  not  known,  but  within  that  portion  which  has 
been  explored  it  appears  to  be  gradually  dying  out  to  the  southward. 
It  is  possible  that  it  may  terminate  at  tlie  Williams  Vein. 

The  most  productive  portion  of  the  Sill  Vein  has  been  between  the 
7th  and  the  450  levels,  where  the  vein  ha.s  been  stoped  tlu'ough  a  length 
of  80  feet,  roughly  1000  tons  of  ore  being  mined  which  averaged  $40 
per  ton. 

Harrell  Vein. 

The  Harrell  Vein  ha.s  been  one  of  the  most  productive  veins  yet 
discovered.  It  strikes  due  north  dipping  to  the  east  at  an  angle 
of  from  60°  to  70°.  The  Harrell  Vein  is  terminated  upward  near 
the  4th  level  by  the  Alpha  Vein  and  the  flat  fault.  To  the  north 
it  terminates  against  the  Antimony  Vein,  while  to  the  south  it  is  termi- 
nated by  the  Flat  Vein  and  the  Williams  Vein.  On  the  9th  level  the 
vein  has  been  explored  for  1000  feet  along  its  strike  within  the  side 
lines  of  the  California  Rand  Silver  Property,  and  what  appears  to  be 
the  same  vein  has  been  explored  for  1100  feet  further  south  in  the 
Bra}-  and  Bisbee  workings  (450-foot  level).  Within  this  distance  the 
vein  gradually  swings  around  until  it  takes  on  a  strike  of  N.  15°  E. 

As  the  vein  is  traced  southward  the  mineralization  appears  to  grad- 
ually decrease,  noticeable  first  by  a  lower  silver  content,  then  by  a 
decrease  in  the  siliceous  gangue  contents  of  the  vein  and  noticeably 
less  alteration  of  the  wall  rocks. 

Near  the  10th  level  the  Harrell  Vein  is  terminated  by  or  merges  with 
the  same  unnamed  flat  vein  which  terminates  the  Sill  Vein.  The  rela- 
tion of  the  Harrell  Vein  to  the  flat  fault  was  .studied  in  some  detail  in 
a  raise  above  the  4th  level.  The  flat  fault  here  showed  several  planes 
of  movement  exposed  in  the  raise.  The  schist  between  the.se  planes  of 
movement  was  so  badly  crushed  as  to  form  a  gouge.  The  Harrell  Vein 
penetrated  through  several  of  these  planes  of  movement  before  stopping, 
being  slightly  offset  along  the  lowe.st  .slip.  The  top  of  the  vein  turned 
slightly  and  paralleled  one  of  the  planes  of  movement  for  a  short  dis- 
tance. Some  brecciated  vein  nuitter  is  scattered  for  short  distances 
througli  the  gouge,  apparently  the  result  of  slight  post-mineral  move- 
ments. In  addition,  the  gouge  is  locally  silicified  and  has  had  deposited 
in  it  small  crystals  of  pyrite.  ai'senopyrite  and  stibnite.  Thase  crystal^ 
though  connnonly  quite  fragile,  are  usually  undisturbed. 

The  Harrell  Vein  possesses  a  well-defined  ore  shoot  which  rakes  to 
the  south  at  an  angle  of  30°  to  the  horizontal  in  the  plane  of  the  vein. 
This  shoot,  which  is  known  to  extend  from  the  4th  to  the  10th  levels. 


—  117  — 

has  a  maximum  width  of  450  feet,  and  a  maximum  length  measured 
horizontally  of  960  feet. 

The  ore  so  far  mined  from  the  Harrell  Vein  has  rang:ed  in  value 
from  ^I'.i  to  $168  per  ton,  prol)al)ly  averaging  in  the  neighborhood  of 
$50.  No  decrease  in  the  tenor  of  the  ore  or  size  of  the  orebody  with 
depth  is  apparent. 

Cow  Trail   Vein. 

Tlie  Cow  Ti-ail  \'ein  is  a  small  vein  segment  striking  .slightly  east 
of  north  wliieh  luei-ges  on  tlie  south  with  th(^  Harrell  Vein  and  on  the 
north  is  terminated  l)y  the  Alpha  Vein.  The  top  of  the  vein  is  in 
contact  with  the  flat  fault  l)etween  tlie  ^rd  and  4th  levels,  while  in 
depth,  the  vein  merges  with  the  Harrell  Vein  between  the  5th  and  6th 
levels.  Comparatively  little  of  the  Cow  Trail  Vein  has  been  stoped, 
the  ore  which  has  been  mined  from  it  coming  ehiefly  from  above  the 
•'•th  level.     The  grade  of  the  ore  was  about  $11.50  per  ton. 

Hughs  Vein. 

Lying  just  west  of  the  Cow  Trail  Vein  and  apparently  merging  with 
it  to  the  south  is  a  vein  known  as  the  Hughs  Vein.  The  limits  of  the 
lluglis  Vein  are  quite  similar  to  those  of  the  Cow  Trail  Vein.  The 
Hughs  Vein  was  much  richer,  however,  having  been  stoped  through 
a  length  of  20  feet  above  the  4th  level,  the  ore  averaging  $27  per  ton; 
for  80  feet  between  the  4th  and  5th  levels,  the  ore  running  $60;  and 
through  60  feet  between  the  5th  and  6th  levels,  the  ore  extracted  being 
worth  ^oii  per  ton. 

Grady   Lease  Vein. 

Following  the  initial  discovery  of  silver  ore  in  the  outcrop  of  the 
shaft  vein,  the  first  discovery  of  silver  ore  on  any  of  the  leases  was  made 
when  the  (Trady  shaft  entered  what  has  since  been  termed  the  Grady 
Lease  Vein. 

The  Grad.y  Lease  Vein  is  abnormal  in  that  it  dips  to  the  west,  though 
nearly  vertical  in  its  upper  part.  It  lies  to  the  east  of  the  Cow  Trail 
Vein  and  strikes  noi-th.  It  is  terminated  upward  between  the  4th 
and  5th  levels  by  the  flat  fault.  To  the  south  it  merges  with  the 
Harrell  Vein,  while  to  the  north  it  terminates  against  the  Alpha  and 
Antimony  Veins.  Along  the  dip,  in  part  above  and  in  part  below  the 
7th  level,  the  Grady  Lease  Vein  forms  a  juncture  with  the  Harrell 
Vein.  While  the  details  of  the  inter.section  are  not  known,  the  writer 
believes  that  the  veins  were  probal)ly  formed  at  the  same  time. 

The  Grady  Lease  Vein  has  been  stoped  through  a  distance  of  approxi- 
mately 200  feet  above  the  5th  level,  the  ore  removed  varying  from  $11 
to  $86  per  ton ;  for  350  feet  between  the  5th  and  6th  levels,  the  ore 
ranging  from  $14  to  $60  per  ton ;  and  for  90  feet  between  the  6th  and 
7th  levels,  the  value  of  the  ore  being  from  $35  to  $154  per  ton. 

Grady  West  Vein. 

The  Grady  West  \'ein  continues  below  the  Harrell  Vein  from  approxi- 

lately  the  line  of  juncture  of  that  vein  with  the  Grady  Lease  Vein. 

U  may  be  a  lower  continuation  of  the  Grady  Lease  Vein.     The  Grady 

''est  Vein,  which  strikes  a  little  east  of  north,  merges  on  the  north  with 

|he  Harrell  Vein  and  on  the  south  with  the  Sill  Vein.     It  appears  to 

)e  bottomed  on  the  9th  level  by  the  flat  lying  and  as  yet  unnamed  vein. 


—  118  — 

The  Grady  West  Vein  has  been  stoped  above  the  7th  level  through  a 
distance  of  approximately  180  feet,  the  ore  removed  ranging  from  $10 
to  $100  per  ton  in  value ;  and  1)ot\veen  the  450  and  7th  levels  for  80 
feet,  the  ore  mined  averaging  $100  per  ton. 

Wark  Vein. 

The  Wark  Vein  roughly  parallels  and  lies  approximately  100  feet 
east  of  the  upper  part  of  the  Grady  Lease  Vein.  It  dips  to  the  east  at 
a  steep  angle.  The  Wark  Vein  is  terminated  upward  between  the  5th 
and  6th  levels  by  the  flat  fault,  while  along  its  dip  it  either  merges 
with  or  is  truncated  by  the  flat  unnamed  vein  near  the  10th  level.  To 
the  south  the  Wark  Vein  proliably  merges  with  the  Harrell  Vein,  while 
to  the  north  it  intersects  or  is  terminated  by  the  Antimony  Vein.  On 
the  7th  level,  the  Antimony  Vein  appears  to  be  cut  by  the  Wark  Vein. 

The  Wark  Vein,  though  possessing  a  maximum  known  length  of 
probably  600  feet,  is  in  part  not  much  more  than  a  stringer,  and  has 
]iot  been  as  productive  as  have  certain  of  the  other  veins.  It  has  been 
stoped  above  the  7th  level  through  a  distance  of  60  feet,  the  ore  removed 
possessing  a  value  of  $17.50  per  ton;  and  above  the  8th  level  through 
a  distance  of  340  feet,  the  ore  ranging  in  value  from  $10  to  $50  per  ton.' 

The  'Unnamed'  Vein. 

This  vein  was  first  recognized  on  the  9th  level,  where  it  truncates 
and  ])ottoms  the  Harrell  and  Grady  West  Veins.  It  strikes  roughly 
north  dipping  40°  E.  Near  the  10th  level,  this  vein  either  bottoms  or 
merges  with  the  Wark  Vein.  It  is  locally  as  much  as  10  to  12  feet  in 
thickness,  and  has  locally  been  productive,  having  been  stoped  near 
the  junctures  with  the  other  veins. 

This  unnamed  vein  cuts  through  the  Antimony  Vein  and  appears  to 
turn  ui)ward,  forming  the  footwall  of  the  Antimony  Vein  between  the 
7th  and  8th  levels.  The  Antimony  Vein  continues  below  where  cut 
by  the  flat  vein,  but  carries  only  traces  of  silver  below  the  intersection. 

Nosser  Vein. 

The  Nosser  Vein,  which  lies  approximately  400  feet  east  of  the  No. 
2  shaft  on  the  8th  level,  has  been  explored  on  the  8th,  9th  and  11th 
levels.  It  strikes  north,  dipping  to  the  east.  The  vein  is  highly 
brecciated  and  in  part  of  large  size,  lieing  approximately  86  feet  thick 
(horizontally)  where  exposed  on  the  10th  level. 

The  Nosser  Vein  appears  to  be  terminated  upward,  above  the  8th 
level,  liy  the  flat  fault,  on  tlie  north  l)y  the  Antimony  Vein,  and  on  the 
south  it  appears  to  pass  througli  the  Williams  Vein,  otfsetting  it  slightly. 

The  Nosser  Vein  has  not  been  a  big  producer,  having  as  yet  been 
stoped  only  through  a  distance  of  280  feet  on  the  8th  level,  the  ore 
removed  ranging  from  $18  to  $134  per  ton;  and  a  small  amount  of 
stoping  on  the  9th  level. 

NO.  6  WORKINGS. 

Although  at  the  time  of  the  writer's  visit  tlie  workings  connected  with 
No.  6  shaft  were  still  in  the  exploration  stage,  several  veins  had  already 
been  developed  whicli  gave  promise  of  becoming  good  producers  of 
silver. 


—  119  — 

The  best  vein  so  far  encountered  is  on  the  720-foot  level.  The  vein, 
which  in*jilaees  is  25  feet  in  thickness,  strikes  N.  25^  E.,  and  dips  from 
40"  to  70  to  the  east.  It  appears  to  pass  to  the  east  of  the  Williams 
Vein  in  the  main  mine  to  the  south. 

This  vein  carries  abundant  miargyrite,  ehietly  deposited  in  drusy 
opcnini.'s  and  brccciated  portions  of  the  gaugue.  The  values  are 
ehietly  in  the  hanging  wall  of  the  vein.  Assays  taken  across  10  feet 
gave  returns  of  75  ounces  of  silver  per  ton. 

This  vein  is  cut  by  another  vein  which  possesses  a  north-south  strike. 

Oil  tlie  next  higher  level,  a  narrow  silver-bearing  vein  was  o])served 
wliich  tlirough  a  portion  of  its  lengtli  possessed  a  schist  hanging  wall 
and  a  diabase  footwall.  Close  to  the  vein  the  diabase  was  highly  altered 
and  cut  by  veinlets  of  siliceous  material  and  pyrite,  the  ferromagnesian 
iiiineraLs  in  the  diabase  l)eing  completely  destroyed.  The  diabase,  on 
assay,  showed  the  presence  of  small  quantities  of  silver. 

PRODUCTION  AND  COSTS. 

From  the  time  of  its  discovery  in  April,  1919,  until  April  1,  1924,  a 
period  of  nearly  tive  >-ears,  the  California  Rand  Silver  Mine  made  a 
gross  i)roduction  of  gold  and  silver  worth  $10,152,666.90.  This  figure 
is  based  on  the  smelter  returns  for  the  ore  and  concentrates  shipped. 
The  milling  recovery  for  the  gold  is  al)out  75%  and  for  the  silver 
about  90%.  The  value  of  the  silver  was  based  on  the  current  market 
prices  at  the  time  of  production.  The  details  of  production  of  the 
pro])prty  to  April  1,  1924,  are  given  in  the  following  table: 

PRODUCTION  RECORD— CALIFORNIA  RAND  SILVER,  INC. 
To  April  1,  1924. 


Tons 

Ounces  gold 

Ounces  silver 

Gross  value 

Shipping  ore 

Milling  ore 

49,1.50.70 
177,074  00 

11,814.589 
12,830.858 

5,212,088.70 
3,383,135.18 

$5,572,154.46 
2,980,532.46 

Mine  total 

Grady  lease -   ._ 

226,224.70 
18,222 .  30 

24,645.447 
5,429  989 

8,595,223.88 
1,487,742.11 

8,552,686.92 
1,599,979.98 

Grand  totals. .  - 

244,447.00 

30,075.436 

10,082,965.99 

$10,152,666.90 

An  examination  of  the  figures  given  in  the  table  shows  that  the 
gold-silver  ratio  in  the  milling  ore  is  approximately  1  ounce  of  gold 
to  264  ounces  of  silver,  whereas  the  ratio  for  the  shipping  ore  (high 
grade)  is  1  ounce  of  gold  to  441  ounces  of  silver.  This  Is  suggestive, 
as  are  the  erratic  gold  assays  obtained  in  many  parts  of  the  mine,  that 
the  gold  and  silver  have  l)een  deposited  by  different  solutions,  a  con- 
clusion already  reached  as  the  result  of  microscopic  study. 

The  di.stinction  between  milling  and  shipping  ore  is  directly  depen- 
dent on  the  market  value  of  silver  at  the  time  of  production.  Pre- 
vious to  June,  1928,  when  as  a  result  of  the  Pittman  Act  silver  Avas 
worth  $1.00  an  ounce,  ore  had  to  contain  70  ounces  or  more  of  silver 
to  l)e  considered  shipping  ore.  Ore  worth  less  than  $70  per  ton  is 
milled  before  shipping.  Both  ore  and  concentrates  are  smelted  at  Selby, 
California. 


—  120  — 


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—  121  — 

The  California  Rand  mill  has  a  daily  capacity  of  400  tons  of  ore. 
The  mill  is  equipped  with  crushers,  2  ball  inills,  2  pebble  mills,  2  classi- 
fiers, flotation  cells  and  settling  tanks.  A  flow  sheet  of  the  mill  is 
given  in  Figure  8. 

The  following  figures,  based  on  the  ore  milled  previous  to  June  1, 
1923,  will  serve  to  indicate  the  milling  efificiency. 

Ore  milled,  tons 97,274 

Average  mill  heads,  per  ton .$17  51 

Average  mill   tails,   per  ton .$2  ()!J 

Average  concentrates,  per  ton .$332  9.^ 

Ratio  of  concentration 21.4>5  to  1. 

Extraction 88.62% 

Tile  nature  of  the  concentrates  may  be  judged  from  their  content  of 
a'i  to  6%  of  arsenic,  and  2%  to  3%  of  antimony. 

The  cost  of  mining,  milling  and  marketing  a  ton  of  ore  from  the 
California  Rand  Silver  ^line,  im-luding  fixed  charges,  is  $12.09  per  ton 
(under  the  conditions  existing  in  the  spring  of  1923).  This  cost  is 
distributed  as  follows: 

Mining $6  46 

Milling 2  25 

Freight     63 

"^r ramming Of5 

Sampling    01 

Smelter  treatment  69 

General    59 

Taxes  60 

Depreciation    SO 

Total   $12  09 

On  the  ba.sis  of  88.69%  extraction,  and  co.sts  as  they  existed  in  the 
spring  of  1923,  the  ore  must  possess  an  initial  assay  value  of  practically 
$14.00  per  ton  before  it  can  be  exploited  at  a  profit. 

The  present  (January  19241  ore  production  amounts  to  from  360  to 
375  tons  daily.  A  total  of  303  men  are  employed,  129  underground 
and  174  on  the  surface. 


YELLOW  ASTER  MINE. 

The  Yellow  Aster  Mine,  the  oldest  mine  and  one  of  the  three  large 
producers  of  the  Randslmrg  (piadrangle,  lies  in  the  quartz  monzonite- 
schist  complex  near  the  top  of  the  Rand  Mountains,  just  south  of 
Randsburg. 

The  property  is  owned  by  the  Yellow  Aster  Mining  and  Milling 
Company  whose  head  office  is  in  Los  Angeles.  No  mining  has  been 
done  by  the  company  for  approximately  six  years,  though  some  ore 
has  been  extracted  during  this  period  by  leasers.  At  the  time  of  the 
writer's  visit  in  January,  1924,  six  leases  were  being  worked  in  the 
mine,  two  men  composing  the  party  working  each  lease.  Leases  within 
the  mine  are  given  on  the  basis  of  a  50%  royalty,  the  company  ifur>ush- 
ing  tools  and  air,  the  leasers  furnishing  their  own  powder  nnd  loaxling 
the  ore  on  cars. 


—  122  — 

In  addition  to  the  leases  Avithin  the  mine,  outside  leases  on  various 
]-)ortions  of  the  property  owned  by  the  Yellow  Aster  Mining  and 
Milling  Company  are  also  given.  At  present  two  of  these  leases  are  in 
operation.  These  outside  leases  pay  a  15%  royalty,  costs  of  haulage 
and  milling  first  being  deducted.  The  leasers  pay  all  costs  incidental 
to  the  mining. 

MINE  WORKINGS. 

Many  of  the  workings  of  the  Yellow  Aster  Mine  are  not  now  acces- 
sible, due  principally  to  the  glory  hole.  For  this  reason  no  attempt 
will  be  made  to  describe  certain  of  the  orebodies.  Descriptions  of 
certain  of  these  may  be  found  in  the  report  of  INTr.  F.  L.  Hess.^ 

The  Yellow  Aster  Mine  is  developed  by  approximately  fifteen  miles 
of  "workings,  and  three  shafts.  The  workings  are  distributed  among 
fourteen  levels,  of  wliieh  the  Rand  level,  the  1st  level  and  the  2nd  level 
are  the  more  important.  Certain  of  the  other  levels  of  the  mine  are 
small  and  unimportant.  The  Rand  level  is  the  main  haulage  level. 
Many  of  the  workings  have  long  since  disappeared  in  the  glory  hole, 
the  limits  of  which  are  indicated  on  the  mine  map,  l*late  4. 

The  collars  of  all  three  shafts  are  on  the  Rand  level.  The  Main 
shaft  sunk  from  the  floor  of  the  glory  hole  is  of  two  compartments, 
250  feet  deep,  which  is  inclined  at  45°  to  the  horizontal.  It  roughly 
follows  down  the  Footwall  Fault,  through  which  it  finally  passes 
before  reaching  the  2nd  level.  The  Hercules  Shaft,  single  compart- 
ment and  450  feet  deep,  is  inclined  at  angles  of  from  35°  to  40° 
to  the  horizontal,  following  down  the  trough  formed  between  the  Jupi- 
ter and  Hanging  \Vall  faults.  The  Rand  Wrtical  Shaft,  two- 
compartment,  and  as  its  name  implies,  vertical,  bottoms  on  the  Footwall 
Fault,  the  collar  of  the  shaft  being  approximately  150  feet  south  and 
we'st  of  the  collar  of  the  Hercules  Shaft.    It  is  450  feet  deep. 

For  many  years  past  all  ore  mined,  excepting  only  the  leasers  ore,  has 
been  withdrawn  through  the  glory  hole.  It  is  planned  to  conduct  all 
future  mining  operations  in  a  similar  manner. 

OREBODIES. 

Tlie  main  orebody  as  now  recognized,  consists  of  a  triangular  block 
of  low-grade  ore,  chiefly  mineralized  quartz  monzoiiite,  which  is  bounded 
on  the  east  by  the  Hanging  Wall  Fault,  on  the  north  by  the  Jupiter 
Fault,  and  on  the  southwest  by  the  Footwall  Fault.  All  of  the  ore  in 
this  block,  down  to  the  loAvest  level  on  which  it  has  l)ee'n  developed, 
namely  the  3rd  level,  is  oxidized  and  free  milling. 

Two  of  the  three  faults  which  liound  the  orebody,  namely  the 
•lupiter  and  Hanging  "Wall  faults,  are  pre-miiieral,  though  ])ost-mineral 
moveincnts  ma\'  have  occurred  along  them.  The  Footwall  Fault  has 
apparently  offset  the  orebody  as  it  was  originally  formed,  for  low- 
grade  sulphide  ore  is  found  to  the  southwest  of  this  fault. 

The  Jupiter  Fault  strikes  approximately  N.  75°  E..  dipping  to  the 
north  at  an  angle  of  about  40"" ;  the  Hanging  Wall  Fault,  which  may 
be  a  curved  continuation  of  the  Jupiter  Fault,  strikes  approximately 
N.  30°  W.,  dipping  45°  NE. ;  the  Footwall  Fault  strikes  N.  60°  W., 
dipping  40°  NE. 

IF.  L.  Hess.     U.  S.   G.   S.  Bull,   430,   pp.   25-31. 


—  123  — 

The  ore  of  the  triani^ular  l)loek  above  referred  to  is  composed  of 
((uartz  nionzonite  (chieHy)  whicli  is  filled  with  a  network  of  quartz 
veink'ts.  The  gold  occurs  both  in  these  veinlets,  and  in  the  quartz 
monzonite  adjacent  to  the  veinlets.  The  (juartz  nionzonite  is  quite 
jiorous  and  badly  iron-staiiUHl.  The  porosity  is  the  result  of  (1) 
the  action  of  the  primary  mineralizins:  solutions,  and  (2)  the  result  of 
oxidation.  Where  neither  mineralized  nor  weathered,  the  <|uartz  mon- 
zonite is  quite  fresh  and  compact.  This  difference  between  the  mineral- 
ized and  unmineralized  (luartz  monzonite  has  resulted  in  the  past  in  the 
reeoi^nition  of  two  'granites.'  an  'older'  and  'badly  altered  granite' 
and  a  'younger  fresh  granite.'  No  evidence  exists  for  more  than  a 
single  intrusion  of  quartz  monzonite,  though  possibly  complex  border 
facies  may  be  locally  developed. 

Cutting  the  triangular  block  which  constitutes  the  present  orebod}^ 
there  formerly  existed  high-grade  orebodies  which  were  largely  worked 
out  early  in  the  life  of  the  property.  These  high-grade  orebodies  may 
be  sul)divided  into  two  groups,  (1)  tho.se  formed  in  vertical  fissures  and 
fracture  zones,  and  (2)  those  formed  beneath  the  low-dipping  pre- 
mineral  faults  which  bound  the  present  low-grade  orebody  on  the 
north  and  east. 

The  high-grade  orebodies  of  the  first  group,  namely  those  formed  in 
vertical  fissures  or  fracture  zones,  were  of  the  same  type  as  the  ma.ss 
of  the  present  low-grade  orebody — but  in  them  the  mineralization  was 
highly  concentrated.  The  fissures  and  zones  in  which  they  formed 
l>robal)ly  represent  the  paths  of  ascent  of  the  mineralizing  solutions. 
From  them  these  solutions  worked  out  into  the  surrounding  fractured 
country  rock,  forming  low-grade  ore  of  the  whole.  Tlie  vertical  ore- 
bodies  strike  northwest.  They  vary  greatly  in  thickness,  from  thin 
veinlets  up  to  the  width  of  over  75  feet  as  stoped  in  the  East  Sets.  They 
stand  about  vertical,  but  due  to  a  series  of  step  faults  which  offset 
them,  they  might  easily  be  mistaken  as  possessing  a  rather  steep  dip  to 
the  northeast.  These  step  faults,  of  which  a  number  occur,  strike 
roughly  northwest,  dipping  at  low  angles  to  the  southwest.  The 
movements  along  them  have  been  roughly  in  the  direction  of  the  dip 
and  of  normal  order.  They  are  apparently  older  than  the  main  move- 
ments on  the  Footwall  Fault,  but  entirely  post-mineral. 

The  largest  of  the  orebodies  formed  in  the  northwest  fissures  and 
fracture  zones  was  that  worked  in  the  East  and  West  Sets,  which  had 
a  combined  length  of  about  80U  feet,  and  a  thickness  of  from  20  to 
75  feet.  This  orebody  was  bounded  on  the  top  and  northwest  by  the 
Jupiter  Fault,  and  was  cut  off  in  depth  and  to  the  south  by  the 
Footwall  Fault. 

The  Rand  Vertical  Vein,  lying  further  to  the  northeast,  possessed 
a  length  of  about  500  feet  and  an  average  thickness  of  15  feet.  It  was 
worked  through  a  depth  of  400  feet. 

The  Price  Vein,  lying  between  the  Rand  Vertical  Vein  and  tlie  East 
and  West  Sets,  was  also  approximately  500  feet  in  length  and  400  feet 
in  depth,  but  averaged  only  10  feet  in  thicknes.s.  Like  the  East  and 
West  Sets  and  the  Rand  Vertical  Veins,  the  Price  Vein  was  bounded 
by  the  Jupiter  and  Footwall  Faults. 

Others  of  the  orebodies  which  occurred  in  zones  striking  northwest 
include  the  Shak'emup.  300  feet  in  length  and  30  feet  thick;  the  Nero, 
60  feet  in  length  and  20  feet  thick ;  the  Coptius,  90  feet  in  length  and 


—  124  — 

25  feet  thick ;  and  the  Blue  Mass.    Other  similar  bodies  we're  undoubt- 
edly mined  in  the  older  workings. 

Tlie  orebodies  of  the  second  type  occur  as  mineralized  zones  under- 
lying the  Jupiter  and  Hanging  Wall  Faults.  These  orebodies  possess 
well-defined  hanging  walls  formed  by  the  gouge  along  the  fault.  The 
ore  grades  out  into  the  rock  below  the  fault  for  distances  as  much  as  20 
feet.  This  ore  is  composed  ordinarily  of  mineralized  country  rock, 
usually  quartz  monzonite  but  sometimes  schi.st,  with  very  little  vein 
quartz. 

The  orebodies  of  this  type  were  long  considered  'drag  orebodies,' 
but  the  rock  constituting  the  ore  usually  preserves  its  original  textures, 
and  though  the  rock  mav  be  badlv  altered  and  fractured  it  is  rarelv 
brecciated  except  immediately  adjacent  to  the  fault. 

Orebodies  of  this  type  occurred  beneath  the  Jupiter  Fault,  along 
the  line  of  the  Midway  Tunnel.  These  were  known  as  the  Stull  Stopes. 
They  were  from  200  to  500  feet  in  length  and  varied  from  four  to 
sixteen  feet  in  thickness,  being  thickest  near  the  surface. 

The  orebodies  adjacent  to  the  Hercules  Shaft,  lying  beneath  the 
inverted  trough  formed  by  the  Jupiter  and  Hanging  Wall  Faults,  also 
belong  to  this  group.  These  bodies  reached  a  thickness  of  over  20  feet, 
thinning,  however,  with  depth. 

The  grade  of  the  ore  which  was  mined  in  the  past  from  these  rich 
veins  is  not  definitely  known.  Some  of  the  ore  taken  out  near  the 
surface  is  presumed  to  have  had  a  value  of  $1,000  per  ton,  or  better, 
these  high  values  probably  being  the  result  of  mechanical  enrichment. 
The  ore  now  being  extracted  by  leasers  from  remnants  and  pillars  of 
these  rich  veins  in  general  has  a  value  of  from  $25.00  to  $50.00  per 
ton,  though  occasionally  some  fortunate  leaser  finds  a  small  shoot  of 
ore  worth  $250.00  per  ton  or  better.  These  values  may  serve  to  illus- 
trate the  grade  of  ore  mined  in  the  early  life  of  the  property. 

The  triangular  block  of  low-grade  oxidized  ore  which  constitutes  the 
present  orebody  may  be  conservatively  estimated  to  contain  a  quarter 
of  a  million  tons  of  ore  actually  in  sight  below  the  glory  hole  between 
the  Rand  level  and  the  2nd  level. 

This  low-grade  ore  is  extremely  spotted.  Assays  var^-  from  a  few 
cents  up  to  $9.00  per  ton.  It  is  estimated  by  the  mine  management  that 
the  run  of  mine  ore  Avill  average  from  $1.00  to  $1.25  per  ton. 

COSTS  AND  PRODUCTION. 

It  is  believed  that  this  low-grade  ore  body  can  be  worked  at  a  profit 
by  means  of  large-scale  operations,  using  glorj'-hole  methods. 

The  ore  can  be  mined  and  passed  through  the  grizzley  at  a  cost  of 
15(^  per  ton  for  mining  and  4^  to  5f'-  per  ton  for  tramming.  Since  the 
mineralized  rock  is  rather  rotten,  and  the  fresh  rock  is  not  mineralized, 
the  oversize  from  a  -l-inch  gri/.zley  can  be  immediately  put  over  the 
dump.  Similarly,  after  crushing  to  ^-inch,  the  plus  ^-ineh  can  be 
discarded.  Thus  for  each  two  tons  mined,  only  one  ton  need  be  milled, 
the  average  gold  content  of  the  ton  milled  liaving  been  raised  to 
$1.75  to  $2.00  per  ton.  The  total  costs  per  ton  milled,  it  is  estimated, 
will  be  approximately  $1.00,  whih*  the  tailings  will  carry  from  30ff  to 
■iO^  pei-  ton. 

A  test  run  or  1000  tons  of  ore  was  being  carried  out  at  the  time  of 
the  writer's  visit.     Should  the  results  be  favorable,  it  is  planned  to 


—  125  — 

install  ball  mills  and  equipment  sufficient  to  mill  250  tons  of  ore  per 
day,  or  the  equivalent  of  500  tons  per  day  mined. 

The  mine  is  now  equipped  with  a  100-stamp  mill,  part  of  which  is 
dismantled.  A  30-stamp  mill  which  formerly  existed  has  been  com- 
pletely dismantled.  Ten  stamps  operate  intermittently  on  the  ore 
mined  by  leasers.  The  ore  is  all  free  milling-,  practically  all  the  ?old 
beintr  caujrht  on  the'  first  two  feet  of  the  plates.  The  <jold  recovered  is 
remarkably  pure,  the  mint  returns  indicating  only  about  5  ozs.  of  silver 
for  each  $1,000  in  gold. 

The  early  production  of  the  Yellow  Aster  Mine  is  only  imperfectly 
known,  since  accurate  records  were  not  kept  for  many  years.  The 
total  production  of  the  i)ropertv  is  estimated  to  have  been  between 
$9,000,000  and  $10,000,000.  Of  this  amount,  approximately  $3,000,000 
has  been  paid  in  dividends. 

PROPERTIES  OF  THE  ATOLIA  MINING  COMPANY. 

The  property  being  operated  bj'  the  Atolia  Mining  Company  consists 
of  some  fifty  patented  claims  on  which  are  located  a  number  of  different 
mines  (see  Plate  3).  The  productive  zone  along  which  most  of  these 
mines  are  located  comi)rises  a  comparatively  narrow  strip  extending 
from  east  to  west  across  the  property  for  a  distance  of  about  two  miles. 
This  zone  appears  to  have  a  maximum  width  of  about  500  feet,  although 
the  parallel  veins  on  which  the  Rainstorm  and  Goldstone  mines  are 
located  and  which  have  boon  ]irnductivo  in  a  small  way.  lie  outside  of 
this  zone. 

The  mineralization  does  not  occur  in  a  single  continuous  vein,  but 
rather  along  a  zone  of  shearing  or  Assuring  which  may  in  a  given 
section  comprise  several  fissures,  roughly  parallel,  but  sometimes  unit- 
ing or  branching.  These  fissures  possess  nearly  the  same  strike  as  does 
the  mineralized  zone  (almost  due  east)  and  dip  at  moderately  steep 
angles  (70°  to  76°)  to  the  north. 

The  tungsten,  occurring  in  scheelite,  together  with  quartz  and  calcite, 
forms  lenticular  masses  of  vein  matter  in  these  fissures.  The  width  of 
commercial  ore  is,  in  general,  from  a  few  inches  to  a  foot,  though  in 
some  places  the  veins  attain  a  width  of  five  feet  or  more. 

The  scheelite  occurs  in  rather  definite  orebodies  which  are  usually 
triangular  in  outline,  witli  the  apex  downward.  The  rake  of  these  ore- 
bodies  is  ordinarily  vertical,  though  the  orebody  on  the  South  Vein 
of  the  Union  Mine  rakes  strongly  to  the  east.  The  mineralization  is 
somewhat  erratic,  even  in  the  recognized  shoots  the  outlines  of  the 
ore?  being  rather  irregular,  the  ore  lensing  out  on  the  margins  of  the 
shoots  in  all  directions. 

The  scheelite  veins  have  suffered  from  post-mineral  faulting  along 
the  fissures  in  which  the  veins  were  formed,  and  also  from  cross  faulting 
which  offsets  the  veins.  The  presence  of  small  quantities  of  scheelite' 
in  some  of  these  north-south  cross  faults  is  suggestive  of  movements 
contemporaneous  with  the  mineralization. 

UNION   MINE. 

The  Union  Mine,  lying  )iear  the  west  end  of  the  productive  belt  on 
the  property  of  the  Atolia  ^Mining  Company,  has  been  the  largest  pro- 
ducer of  any  of  the  scheelite  mines.  Two  veins  have  been  worked  in 
this  mine,  the  North  Vein  and  the  South  Vein. 


—  126  — 

This  mine  is  developed  by  six  shafts  and  over  two  miles  of  horizontal 
workino's  distributed  throufrh  eleven  levels.  The  working  shaft  is  the 
Xew  No.  1  Main  Shaft  which  is  1050  feet  deep,  measured  on  the  incline. 

The  ore  shoot  on  the  Xoi'th  Vein  was  1100  feet  in  leng'th  on  the 
surface,  fading  out  at  a  depth  of  100  feet  on  either  end,  but  extending 
downward  near  the  center  for  700  feet,  measured  along  the  vein. 

Tlie  South  Vein  was  discovered  underground  in  1916,  being  a  blind 
vein  which  did  not  outcrop.  This  vein  has  been  the  richest  and  largest 
producer  yet  discovered,  having  actually  produced  more  units  of  WO., 
than  all  other  kno'wai  veins  of  the  district  combined.  The  grade  of  the 
ore  mined  from  it  was  unusually  high.  The  vein  varied  in  thickness 
from  1  to  5  feet,  though  in  one  place  it  attained  a  thickness  of  17  feet. 
The  South  Vein  was  stoped  upward  to  between  the  3rd  and  4th  levels 
where  it  disappeared.  It  has  been  opened  downward  to  the  10th  level. 
The  ore  shoot  in  the  South  Vein  is  triangular  in  outline,  raking  strongly 
to   the   east. 

At  present,  both  ends  of  all  drifts  on  the  North  and  South  Veins  are 
barren  on  the  9tli  and  on  all  higher  levels,  so  that  the  limits  of  ore 
are  apparently  everywhere  determined  above  the  10th  level. 

AMITY   MINE. 

The  Amity  Mine  adjoins  the  Union  Mine  on  the  east.  It  is  developed 
by  three  shafts,  the  deepest  being  200  feet,  and  by  approximately  1100 
feet  of  drifts  and  crosscuts  distributed  through  three  levels.  The  work- 
ings follow  both  the  North  and  the  South  Veins. 

The  ore  shoot  in  which  the  workings  are  located  is  in  the  South  Vein. 
It  was  bottomed  at  a  depth  of  175  feet,  the  ore  pinching  out  in  all 
directions.     The  Amity  Mine  was  abandoned  previous  to  1916. 

AXILLA    MINE. 

The  workings  of  this  property,  which  consist  of  a  50-foot  shaft  and  a 
110-foot  drift,  follow  the  North  Vein.    No  ore  has  been  found. 

ACALEY   MINE. 

Developed  by  two  shafts,  the  deepest  being  140  feet,  and  approxi- 
mately 350  feet  of  drifts,  distributed  through  four  levels.  The  work- 
ings follow  the  North  Vein.  The  ore  shoot  on  which  the  work  was  done, 
extended  onh^  to  a  depth  of  100  feet. 

PAPOOSE   MINE. 

The  workings  of  the  Papoose  Mine  are  not  now  accessible,  due  to 
caving.  They  consist  of  three  shafts,  the  deepest  being  320  feet,  and 
approximately  2600  feet  of  drifts  distributed  through  six  levels.  The 
ore!  shoot  which  Avas  being  worked  in  this  mine  M'as  cut  off  just  above 
the  4th  level  at  a  depth  of  190  feet  by  a  tiat  fault.  No  ore  was  found 
on  the  two  lower  levels. 

MAHOOD   MINE. 

The  workings  of  this  mine  are  located  along  a  vein  paralleling  the 
Papoose  Vein.  The  ore  in  general,  reached  the  first  level  only  in  spots, 
though  in  one  place  it  reached  the  second  level.  The  mine  is  developed 
by  about  350  feet  of  drifts,  divided  between  the  two  levels. 


—  127  — 

FLAT   IRON    MINE. 

Developed  by  four  shafts,  tlio  deepest  beinji:  175  feet,  and  by  al)()ut 
1100  feet  of  drifts  distributed  amonw  four  levels.  Ore  extended  in 
places  to  a  de]itli  of  ISO  feet.  The  mine  was  exhausted  previous  to  1!)!."). 
The  workiii'^s  arc  not  now  accessible. 

PAR   MINE. 

Developed  by  foui-  shafts,  the'  (h'epest  200  feet,  and  by  approximately 
lyOO  feet  of  drifts.    There  are  four  levels.    No  ore  extended  below  the 
.'h'd  level.     The  ore  grades  out  to  the  east  and  practically  so,  becoming 
very  erratic,  to  the  west. 

GOLDSTONE    MINE. 

The  workings  of  this  property  ai-e  outside  of  the  main  productive 
zone  on  a  vein  which  roughly  parallels  that  zone.  The  property  has 
not  been  operated  since  1914. 

RAINSTORM    MINE. 

The  Rainstorm  Mine  is  on  a  vein  to  tiie  north  of  but  ])arallel  to  the 
main  productive  zone.  The  workings  are  150  feet  deep.  The  vein, 
which  is  about  six  inches  wide,  carries  some  scheelite  and  considerable 
stibnito.  A  gold  pocket,  worth  $600  to  $700  was  taken  from  tlic  out- 
crop of  the  vein.     The  property  was  abandoned  before  ]i)15. 

PRODUCTION. 

The  total  production  from  the  ])ropertics  owned  by  the  Atolia  Mining 
Company  up  to  the  time  they  Avere  shut  doAAni  on  March  1,  1919, 
fajiproximately  18  years  production),  amounted  to  514,382  units  of 
AVO..  This  was  contained  in  high-grade  ore  and  concentrates  having 
an  average  composition  of  about  70%  WO... 

Tlie  average  ore  which  has  been  mined  from  the  pr()j)erties  has  varied 
from  3^%  to  as  high"  as  8%  of  contained  WO.^.  Exceptionally,  ore 
containing  as  high  as  60%  to  70%  of  contained  WO,  has  been  mined 
and  shipped  without  further  ti'eatment.  The  lower  grade  ores  have 
been  concentrated  in  the  comi)any's  mill  at  Atolia  previous  to  shipment 
as  concentrates. 

The  following  tabulation  will  serve  to  indicate  the  production  and 
variation  in  the  WO.,  content  of  the  ore's  as  well  as  extraction  and  cost 
data  for  the  10  years  of  production  previous  to  1919  : 


Year 

Tons  ore 
mined 

WOs  content, 
per  cent 

Per  cent 
recovery 

Unit  cost 

Unit  selling 
price 

1909     .   .   -. 

5,182 

6,780 

4,8.i6 

8,043 

7,592 

4,829 

8,994 

17,406 

22,064 

28,071 

7.51 
5.06 
4.79 
4.47 
5.85 
8.04 
7.86 
8.37 
6.11 
3.38 

82.90 
80.03 
72.65 
72.49 
69.37 
75 .  56 
76.40 
75.02 
78.80 
70.30 

$2  09 

3  26 
2  56 

4  73 
4  99 

6  13 

7  68 

4  25 

5  19 
9  47 

S5  83 
8  48 

1910 

1911-   ----..   .- 

6  37 

1912 

8  10 

1913 

7  98 

1914 

1915 

1916 

1917 

1918 

6  50 
14  03 
33  74 
18  54 
25  11 

—  128  — 

Commencing  January,  1924,  following  nearly  five  years  of  idleness, 
the  Atolia  properties  were  reopened  on  a  leasing  basis,  and  a  number 
of  leases  are  now  in  operation. 

OTHER  PROPERTIES. 

BALTIC. 

The  Baltic  property,  owned  by  the  Rand  Mining  and  Milling  Com- 
pany, is  located  approximately  one  and  one-half  miles  southeast  of 
Randsburg,  in  the  old  Stringer  District.  The  property  is  developed 
by  a  shaft,  inclined  at  a  low  angle  to  the  north,  which  reached  a  depth 
of  162  feet.  Two  veins  were  worked,  one  of  which  is  said  to  strike  east, 
and  the  other  north.  The  veins  intersected  near  the  point  where  the 
shaft  was  sunk.  Some  good  ore  was  removed  between  the  bottom 
of  the  shaft  and  the  surface,  but  no  ore  was  found  below  a  depth  of 
162  feet.  The  property  has  not  been  worked  for  many  years.  It  is 
equipped  with  a  10-stamp  mill. 

Following  the  silver  discovery  in  1919,  a  new  shaft  was  sunk  approxi- 
mately 600  feet  northwest  of  the  old  shaft,  on  a  continuation  of  the 
vein  being  worked  on  the  K.  C.  N.  Lode  Claim.  This  shaft  (l^-com- 
partment)  is  inclined  to  the  south  at  an  angle  of  65°  and  is  610  feet 
deep  as  measured  on  the  incline.  Levels  were  cut  at  300  and  580  feet. 
The  300-foot  level  crosscut  95  feet  to  the  south,  intersecting  the  vein  at 
55  feet ;  230  feet  of  drifts  were  run  along  the  vein.  On  the  580-foot 
level,  crosscuts  were  run  112  feet  to  the  south  and  96  feet  to  the"  north, 
but  the  vein  was  not  found. 

The  vein,  where  prospected  on  the  300-foot  level,  varies  in  width 
from  2  feet  to  4  feet,  but  carries  no  commercial  ore.  This  property  was 
closed  down  in  July,  1923.  The  Monarch  Rand  Minins;  Company  have 
since  acquired  the  Baltic  claim. 

The  Rand  Mining  and  Milling  Company  also  owns  the  Buckboard 
property,  located  approximately  two  miles  southwest  of  the  Baltic 
Mine.  This  property  is  developed  by  a  single-compartment  shaft 
inclined  at  a  low  angle  to  the  northeast.  It  has  not  been  operated  for 
many  years  but  at  one  time  produced  more  or  less  gold. 

BEEHIVE. 

The  Beehive  property,  comprising  a  group  of  ten  claims,  is  located 
on  the  south  slope  of  the  El  Paso  Mountains  across  the  vally  to  the 
north  from  Randsburg.  The  property  has  been  developed  by  four 
shallow  shafts  and  approximately  400  feet  of  horizontal  workings.  As 
yet  no  orebody  has  been  discovered,  but  assays  made  on  samples  taken 
from  small  stringers  which  the  workings  have  been  following,  show 
good  values  in  lead,  silver  and  gold.  The  property  is  ownied  by  the' 
Kern  Rand  Mines,  Inc.    No  work  is  now  being  done. 

BELCHER   EXTENSION. 

This  property,  located  to  the  southwest  of  the  California  Rand  Silver 
Mine,  is  operated  by  the  Belcher  Extension  Mining  Company,  Inc. 
The  property  is  developed  by  a  vertical,  IJ-compartment  shaft,  432 
feet  deep,  and  b}^  approximately  300  feet  of  horizontal  workings  dis- 
tributed between  three  levels  at  depths  of  232,  332  and  432  feet. 

Three  veins  were  cut  in  the  shaft.  These  were  prospected  on  the 
several  levels  and  found  to  consist  of  vein  matter  quite  similar  to  the 


—  129  — 

silver-producing:  veins  of  the  district.  Locally,  they  carried  as  mueli 
as  '2-i-  oz.  of  silver  and  20<'  gold  per  ton,  but  as  yet  no  orebody  has 
been  found. 

The  iiropcrty  is  not  now  bein^'  worked,  but  it  is  stated  that  furtlier 
exploi'ations  A\ill  be  attenii)ted   in  the  near  future. 

BEN    HUR. 

The  J^en  Ilur  property.  eoni])risini;-  a  sing-le  patented  claim,  was 
operated  by  the  Ben  Ilur  Divide  Minin<^  Company.  The  property  is 
developed  by  a  vertical,  1-J-eompartment  shaft,  400  feet  deep.  Levels 
occur  at  200  feet,  with  350"  feet  of  workings;  300  feet,  with  olo  feet  of 
workings;  and  400  feet,  with  !)10  fe(4  of  working's. 

Tiiree  veins  which  occur  on  the  property  were  thoroughly  prospeeted 
by  these  workings.  The  veins  possessed  strikes  from  north  to  north- 
east, and  faii'ly  steep  dips  to  the  east  and  southeast.  They  varied  i)i 
thickness  from  mere  stringers  up  to  12  feet  or  mor(>.  The  vein  matter 
consisted  of  the  usual  bluish-gray  siliceous  gangue,  which  locally  carried 
small  quantities  of  silver  minerals. 

Although  severely  criticized  by  the  local  press  for  their  action,  the 
opei-ators  of  the  Ben  Ilur  in  1923,  after  having  thoroughly  prospeeted 
these  veins  and  finding  them  valueless,  proi)erly  proceeded  to  slmt 
down  tli(>  property  and  dismantle  its  equipment. 

BEN    HUR   EXTENSION. 

This  property,  which  lies  a  short  distance  southeast  of  the  Baltic 
mill,  was  prospected  by  a  vertical  shaft  100  feet  deep,  and  a  drift  240 
feet  in  length  extending  northwest  from  the  bottom  of  the  shaft.  Sev- 
(M'al  stringers  were  cut  which  showed  the  jiresence  of  traces  of  gold. 

The  property  was  taken  over  in  the  fall  of  1923  by  the  IMonai'ch 
Rand  Mining  Company. 

BEVIS   DIVIDE. 

This  property,  worked  by  the  Bevis  Divide  Mining  Company,  consists 
of  a  lease  on  a  small  portion  of  the  gi'ound  held  by  the  Pittsburg  and 
Mt.  Shasta  Mining  Company.  The  Bevis  Divide  shaft  lies  about  1200 
feet  to  the  west  of  the  new  shaft  of  that  company.  It  consists  of  a 
vertical.  H-compartment  shaft,  150  feet  deep.  No  veins  were  discov- 
ered and  the  property  was  not  operating  in  1923. 

BIG   FOUR. 

The  Big  Four  shaft  was  sunk  about  3300  feet  east  by  north  from  the 
California  Rand  Xo.  2  shaft  by  the  Rand  Consolidated  Silver  Mining 
Company,  Inc.  The  shaft  (2^  compartments),  which  is  now  1085  feel; 
deep,  has  been  in  sandstones  of  the  Rosamond  formation  throughout 
this  depth.  Diabase  and  rhyolite  ix'bbles  are  found  in  the  sandstone  at 
the  bottom  of  the  shaft.  The  stratification  has  had  a  dip  to  the  west 
of  40°  to  50°  throughout  most  of  the  depth  of  the  shaft,  and  at  the 
bottom  of  the  shaft  what  appear-gd  to  be  lines  of  stratification  shov.'ed 
a  westerly  dip  of  aj^proximately  50°. 

Work  in  the  shaft  was  suspended  August  1,  1923,  and  has  not  as 
yet  been  resumed. 

9—37841 


—  130  — 

BIG  GOLD. 

The  BifT  Gold  property,  composed  of  five  claims,  worked  under 
option  by  the  Big  Gold  Company,  lies  hig:h  np  on  the  north  slope  of 
the  Rand  ^Mountains,  about  a  mile  southwest  of  Randsburu'.  The  recent 
workings  on  the  property  consist  of  a  vertical,  li-compartment  shaft, 
884  feet  in  depth,  and  over  500  feet  of  horizontal  workings.  From  the 
surface  doAvn  to  145  feet,  the  shaft  is  in  quartz  monzonite,  145  to  155 
feet  in  quartz  latite,  and  from  155  feet  to  the  sump  in  schist. 

Most  of  the  workhigs  have  been  run  along  a  vein  underlying  a 
strong  fault.  The  fault  plane,  which  strikes  N.  2€°  W.,  and  dips  to  the 
west,  shows  a  well-developed  gouge  and  is  strongly  striated,  the  striae 
being  vertical.  The  vein  was  intersected  in  the  shaft  at  a  depth  of 
155  feet.  At  this  point  it  was  4  feet  thick  and  possessed  a  quartz  latite 
lianging  wall  and  a  schist  footwall.  The  vein  is  in  general  badly 
brecciated.  Assays  as  high  as  $18.00  per  ton  in  gold  have  been  obtained 
from  this  vein.  The  gold  appears  to  be  very  fine.  The  presence  of  some 
tellurium  in  the  ore  is  also  reported,  though  in  what  form  it  occurs  is 
not  known. 

In  addition  to  the  vein  just  described,  two  east-west  veins  occur  Avhich 
are  about  300  feet  apart.  These  have  given  assays  of  from  5  oz.  to  8  oz. 
of  silver  per  ton. 

The  property  was  shut  down  during  the  fall  of  1923. 

BIG  SIX. 

A  small  property  lying  east  of  the  railroad  and  approximately  3000 
feet  south  of  Hampton.  The  shaft,  after  passing  through  alluvium 
and  Rosamond  sandstones,  entered  the  quartz  monzonite  at  a  depth  of 
250  feet  from  the  collar.    Shortly  after  this  the  work  was  suspended. 

BLACK  HAWK. 

The  Black  Hawk  Mine  lies  near  the  highway  about  2^  miles  south- 
east of  Randsburg.  The  property  is  owned  by  the  Pittsburg  and  Mt. 
Shasta  Mining  Company.  The  property  is  developed  by  an  inclined 
shaft  250  feet  in  depth.  Levels  are  opened  at  depths  of  50,  100,  200 
and  250  feet.  There  are  approximately  3000  feet  of  horizontal  work- 
ings, principally  to  the  southeast  and  west  of  the  shaft. 

Two  prominent  parallel  veins  occur,  which  strike  N.  55°  W.  and  dip 
65°  NE.  The  values  are  chiefly  confined  to  the  northern  vein  which 
is  folloAved  by  the  shaft.  The  main  vein  averages  about  10  inches  in 
thickness ;  the  southwestern  vein  over  a  foot,  varying  from  one  to 
nearly  two  feet  in  places.  The  veins  are  unusual  for  this  district  in 
being  composed  of  quartz  throughout.     The  wall  rocks  are  schist. 

The  veins  are  al)undantly  faulted  l)y  a  minor  but  complex  fault 
system  which  appears  to  have  been  decipliered  by  the  mine  manage- 
ment. The  faults,  of  wliieli  three  are  recognized,  strike  in  the  northeast 
quadrant,  dipping  to  the  southeast.  The  west  side  of  the  faults  have 
moved  south. 

Most  of  the  ore  mined  has  ei)me  from  above  the  2nd  level,  l)eing  free 
milling.  Sulphides  appear  on  the  2nd  level.  The  mill  ore  has  an 
average  value  of  about  $15.00  per  ton.  All  the  ore  mined,  as  well  as 
some  custom  ore,  is  milled  in  a  5-stamp  mill  located  on  the  property. 
The  bullion  obtained  has  a  fineness  of  730  to  760  as  indicated  by  the 


—  131  — 

•  mint  returns.  The  total  production  from  the  lUjick  llawk  has  boon  in 
the  neighborhood   of  $350,000. 

Following:  the  silver  discovery  in  1!)15),  the  Pittsl)urg  and  Mt.  Shasta 
Mining  Company  sank  a  shaft  in  the  northeast  part  of  their  lioldings, 
about  2400  feet  south  of  th.'  California  Rand  No.  2  shaft.  This  shaft 
is  vertical,  of  2  comjiailmciits  and  TOO  feet  dccji.  Schist  was  struck 
at  a  depth  of  110  feet. 

A  cros.scut  was  driven  fi'om  the  bottom  of  the  shaft  for  450  feet  to 
tlie  west  but  intersected  no  veins.  A  crosscut  to  tlie  east,  315  feet  in 
length  cut  through  two  veins,  one  at  the  face,  4  feet  wide,  striking 
northeast  and  dipping  70°  east,  carrying  a  trace  of  silver;  the  other 
a  1^  foot  breceiated  zone,  witliout  any  siliceous  vein  matter,  but  carry- 
ing a  trace  of  gold  and  silver,  wliich  strikes  N.  20°  E.,  dipping  55°  SE. 

Work  was  discontinued  in  tlie  new  shaft  late  in  1923.  Tlie  Black 
Hawk  Mine  is  operating  in  a  small  way. 

BRAY  AND   BISBEE. 

The  Bray  and  Bisbee  property,  comprising  two  claims  adjoining  the 
California  Rand  Silver  and  Coyote  in-opertics  on  tlie  soutli,  is  owned 
by  the  Rand  Silver  King  Mining  Compan\'.  The  properly  is  now  sliut 
down  but  may  be  reopened. 

Th0  property  is  developed  by  a  1^-compartment  vertical  shaft,  587 
feet  deep,  which  is  located  1400  feet  south  of  the  California  Rand  No.  2 
shaft,  and  by  approximately  5000  feet  of  drifts  and  crosscuts  dis- 
tributed between  four  levels.  (See  Plate  2.)  The  450-foot  level  is 
the  principal  level,  corresponding  to  the  9th  level  of  the  California 
Rand  Silver  Mine  and  connecting  with  that  level  through  the  5th 
level  of  the  Coyote  Mine. 

Certain  of  the  veins  developed  in  the  California  Rand  Silver  and 
Coyote  workings  to  the  north  are  found  to  continue  south  into  the 
Bray  and  Bisbee  workings.  These  include  veins  of  both  the  northeast 
system  and  of  the  north-south  system. 

Locally  the  veins  of  both  systems  carry  values  sut^cient  to  form  small 
orebodies,  but  much  of  the  vein  matter  as  now  exposed  must  be  classed 
as  being  too  low  in  grade  to  constitute  oi-e. 

The  vein  filling  is  (juite  similar  to  that  of  the  veins  of  the  California 
Rand  Silver  Mine  to  the  north  and  many  of  the  veins  are  of  good  size. 
But  a.s  the  veins  are  traced  from  the  northern  part  of  the  workings 
south  there  seems  to  be  a  diminution  in  the  amount  of  vein  matter 
which  has  been  de{)Osited,  in  the  silver  content  of  the  veins,  and  in  the 
silicification  and  alteration  of  the  schist  wall  rocks,  as  though  to  the 
southward  the  mineralizing  solutions  had  been  less  and  less  active. 

Perhaps  the  best  ore  exposed  in  the  Bray  and  Bisbee  w^orkings  is 
found  on  the  450  foot  level  in  a  vein  striking  N.  55°  E.,  and  passing  50 
feet  to  the  northwest  of  the  shaft.  For  a  distance  of  100  feet  this  vein 
varies  from  2^  to  5  feet  in  thickness.  Where  first  encountered  it 
averaged  19  oz.  of  silver  across  5  feet.  This  vein  is  cut  off  to  the  north- 
east and  also  2'()  feet  above  the  level.  To  the  southwest  it  intersects  or 
merges  with  a  vein  strikintr  N.  15°  E.  which  may  be  a  continuation  of 
the  Han-ell  Vein. 

A  prominent  line  of  faulting  known  as  the  Fault  Vein,  which  strikes 
about  north  and  stands  nearly  vertical,  passes  through  the  workings. 


—  132  — 

Locally  it  forms  a  zone  20  feet  thick.  This  zone  passes  just  east  of 
the  shaft  on  the  5th  level,  through  the  shaft  on  the  450  level,  and  60 
feet  east  of  the  shaft  on  the  600  level.  It  does  not  appear  to  he 
mineralized,  but  oifsets  other  mineralized  veins. 

The  flat  eastward-diiiping  fault,  which  was  recognized  in  the  Cali- 
fornia Rand  Silver  Mine  capping  the  ore,  is  also  present  in  the  Bray 
and  Bishee  workings,  being  exposed  on  the  3rd  level,  apparently 
cutting  tlie  .shaft  jiLst  al)0ve  that  level. 

BULLY   BOY. 

The  Bully  Boy  property,  composing  7  claims  totaling  110  acres, 
is  located  nearly  two  miles  due  south  of  Randsburg.  The  property  is 
operated  by  the  ITnited  Mines  Company,  Inc.  The  property  is  devel- 
oped by  four  shafts  and  over  2000  feet  of  old  underground  openings, 
most  of  which  are  inaccessible.  Of  the  shafts,  two  are  old  and  inacces- 
sible, one  has  recently  been  deepened  to  100  feet,  and  the  4th,  vertical, 
is  now  down  70  feet  and  still  sinking. 

Most  of  the  work  on  the  jiroperty  has  been  done  on  a  narrow  vein 
which,  though  narrow,  varied  considerably  in  thickness  and  is  said  to 
have  carried  good  values.  ]\Iueh  of  the  upper  part  of  this  vein  was 
stoped  years  ago.     The  vein  strikes  N.  65°  E..  dipping  53°  N. 

The  claims  held  by  the  United  Mines  Company  are  credited  \nth  a 
past  production  of  about  $120,000  in  gold. 

BUTTE. 

The  Butte  Mine,  located  just  east  of  Randsburg,  has  not  been  worked 
for  a  number  of  years.  The  mine  is  equipped  with  a  10-stamp  mill 
using  plate  amalgamation. 

The  ore  which  has  in  past  years  l)een  mined  from  tlie  Butte  property 
occurred  as  quartz  veins  and  lenses  and  as  mineralized  schist  intimately 
associated  with  the  large  diabase  dike  which  crosses  the  property.  It 
is  stated  that  the  ore  occurred  chiefly  on  the  footwall  of  the  dike, 
though  in  places  it  cuts  through  the  dike. 

The  Butte  is  credited  with  a  past  production  of  gold  stated  to  be 
in  e^xcess  of  $500,000. 

CHICKEN    HAWK. 

Developed  only  ])y  a  shaft  located  just  west  of  the  railroad  and 
nearly  a  mile  south  of  Hampton.  The  shaft,  after  passing  through 
204  feet  of  alluvium  and  Rosamond  sandstones,  entered  the  quartz 
monzonite.  shortly  after  which  the  work  was  discontinued. 

CIMA    BIMETALLIC. 

Developed  only  by  a  l|-compartment  vertical  shaft,  200  feet  deep, 
and  apparently  entirely  in  the  Rosamond  formation.  Water  stands 
in  the  shaft.  No  recent  work  has  been  done.  The  property,  which  is 
owned  by  the  Randsburg  Cima  Bimetallic  Company,  is  located  just 
east  of  Johannesburg. 

CONSOLIDATED. 

The  property  of  the  Consolidated  Mines  Company  is  located  at  the 
eastern  edge  of  Randsburg.     No  work  has  been  done  since  the  war. 


—  133  — 

The  i)roperty  is  developed  l)y  ;i  single  eompartment  shaft  inclined  to 
llie  north.  The  mine  possesses  a  i)artly  dismantled  10-stam])  mill. 
X(i  record  of  tiie  production  of  the  property  could  he  ohtained. 

COYOTE. 

The  Randshurg  Silver  JNIining  Compan\ .  Inc..  liohls  16  claims  or 
fractions  located  to  the  southeast,  nortlieast  and  northwest  of  the 
California  Rand  Silver  property.  The  chief  workings  of  the  company 
ai-e  in  the  Coyote  Mine.  The  Coyote  Shaft,  1^-compartment.  vertical, 
and  730  feet  deep  is  located  500  feet  southeast  of  tlie  Califoi'uia  Rand 
No.  2  shaft.  There  are  over  6000  feet  of  workings  in  the  Coyote  Mine, 
distributed  through  five  levels  (see  Plate  2).  The  principal  workings 
are  071  the  5tli  level. 

Pi'ohahly  the  best  ore  is  found  on  the  -Itli  level  where  a  crosscut  and 
drift  to  tlie  southwest  of  the  shaft  have  exposed  the  southern  con- 
tinuation of  the  Harrell  Vein.  The  drift  follows  the  vein  for  over 
300  feet,  the  vein  probably  averaging  '■]  feet  in  thickness.  "What 
appears  to  be  the  same  vein  in  part  is  also  shown  in  a  drift  southwest 
from  the  shaft  on  the  6th  level. 

A  second  vein  was  encountered  close  to  the  shaft  on  the  5th  level, 
the  veiii  sti'iking  X.  12°  E.,  and  averaging  about  2  feet  in  thickness. 
Tlie  continuation  of  the  vein  on  the  6tli  level  was  not  posiliv(dy 
identified. 

The  thii'd  vein  exposed  on  the  5th  level  is  the  ('oyote  East  Vein, 
striking  X.  20°  E..  and  passing  about  200  feet  east  of  the  shaft  on  this 
level.  Tills  vein  was  (ii'st  intersected  in  a  crosscut  run  due  east  from 
the  shaft.  The  crosscut  went  200  feet  further  east  and  then  over  500 
feet  southeast  without  intersecting  any  other  veins.  It  probal)ly  cuts 
through  the  flat  fault  which  would  account  for  the  dearth  of  veins 
further  east,  no  veins  being  known  to  occur  in  the  hanging  wall  of  the 
flat  fault.  The  flat  fault  is  said  to  cross  the  shaft  between  the  3rd  and 
4th  levels. 

From  the  point  of  intei-seetion  of  the  east  crosscut  on  the-  5th  level 
with  the  Coyote  East  ^'ein,  drifts  were  run  for  250  feet  to  the  north, 
good  ore  being  exposed,  and  nearly  500  feet  to  the  south  along  the  vein. 
About  200  feet  to  the  south,  the  .silver  minerals  which  furtln'i-  north  are 
e'asily  visible,  gradually  disappear. 

The  Coyote  Xo.  2,  Kelly  Xo.  1,  or  Foster  Sliaft,  as  it  is  variously 
known,  was  sunk  875  feet  north  by  east  from  the  California  Rand  No. 
2  shaft.  The  shaft  is  1%  compartment,  vertical,  and  450  feet  deep. 
750  feet  of  drifting  was  done  on  the  350  foot  level  parallel  to  the  Cali- 
fornia Rand  side  line.  Xo  veins  were  encountered.  The  drift  is  all  in 
schist  except  the  northeast  end  which  is  said  to  have  entered  the  quartz 
mouzonite. 

Seven  hundred  feet  to  the  northeast  is  the  Elder-Gustave  Lease  Shaft, 
H-compartment,  vertical,  and  230  feet  in  depth.  The  lower  part  of  the 
shaft  is  in  the  quartz  monzonite.     No  drifting  was  done. 

Seven  hundred  feet  farther  northeast  is  the  so-called  Thirteen  Lease 
Shaft,  and  400  feet  still  farther  is  the  Silver  Horde  Lease  Shaft.  The 
latter  is  vertical,  1-^-compartmeiit,  and  340  feet  in  depth.  A  110-foot 
drift  extends  from  the  bottom  of  the  shaft  northward.  It  is  not  known 
whether  these  workings  are  in  silicified  Rosamond  sandstone,  rhyolite 


—  134  — 

or  quartz  inonzonite.  The  only  material  observed  on  the  dump  con- 
sisted of  silicified  Rosamond  sandstone. 

The  Fox  No.  2  Shaft  is  400  feet  north  of  the  California  Rand  No.  6 
shaft.  It  was  sunk  on  eompanj^  account,  being  a  2-compartment 
vertical  shaft.  It  reached  a  depth  of  260  feet  but  did  not  pass  through 
the  Rosamond  formation. 

The  Santa  Fe  Shaft  lies  400  feet  farther  east  in  the  midst  of  Inn 
City.  It  also  wa.s  sunk  by  the  Randsburg  Silver  Mining  Company, 
being  a  l|-compartment,  vertical  shaft,  and  410  feet  in  depth.  It 
also  is  entirely  within  the  Rosamond  formation. 

No  M'ork  has  been  done  recently  on  any  of  the  holdings  of  the  Rands- 
burg Silver  ^Mining  Company,  with  the  exception  of  the  Santa  Fe  shaft. 

CUVE. 

The  Rand  United  IMining  Company  are  working  the  Cuve  group 
through  the  shaft  of  the  ^lizpah  ^lontana.  The  Cuve  group  consists  of 
the  Cuve  claim  and  six  claims  to  the  north  which  are  held  under  option. 

FLAT  TIRE. 

The  Southern  IMining  and  IMilling  Company  holds  14  claims  known 
as  the  Flat  Tire  group  lying  to  the  north  of  the  Big  Four  property. 
Shaft  sinking  was  started  in  July,  1923.  The  shaft  is  located  2400  feet 
north  of  the  Big  Four  Shaft,  and  is  a  vertical,  24-compartment  shaft. 
On  January  1,  1924,  the  shaft  was  down  284  feet,  all  in  the  Rosamond 
formation.  The  company  has  announced  its  intention  of  sinking 
to  a  depth  of  1000  feet  if  necessary  in  order  to  prospect  the  underlying 
quartz  monzonite. 

FOX   LEASE. 

The  Fox  Lease  Shaft  was  sunk  on  ground  held  by  the  Randsburg 
Silver  Mining  Company.  The  shaft  is  vertical,  1^  compartments, 
775  feet  deep,  and  is  900  feet  northwest  of  the  California  Rand 
No.  6  Shaft.  This  shaft  passed  through  about  400  feet  of  Rosamond 
strata,  below  which  it  is  in  cpiartz  monzonite.  A  crosscut  1150  feet  in 
length  was  driven  southeast  from  the  bottom  of  the  shaft. 

Three  veinlets  carrying  silver  were  intersected  at  distances  of  107, 
250  and  265  feet  from  the  bottom  of  the  shaft.  All  had  strikes  of 
approximately  north,  dipping  at  moderately  steep  angles  to  the  east. 
At  a  distance  of  250  to  300  feet  from  the  shaft  the  crosscut  entered 
the  schist.  At  560  feet,  a  large  breeciated  vein  11  feet  thick  was 
cut  which  assayed  5  oz.  of  silver  per  ton.  An  odorless  and  color- 
less gas  which  extinguishes  a  flame,  apparently  carbon  dioxide,  is  issue- 
ing  from  this  vein.  This  vein  is  (|uite  likely  the  Antimony  Vein  with 
which  it  apparently  lines  up.  A  diabase  dike,  2  to  3  feet  thick  was  cut 
at  742  feet.  It  gave  assays  of  0.8  oz.  of  silver  per  ton.  At  850  feet  the 
crosscut  passed  througli  the  tint  fault,  and  at  1100  feet  entered  the 
Rosamond  formation.  The  face  of  the  short  drift  which  extends  north 
from  the  crosscut  is  also  said  to  have  entered  the  zone  of  the  flat  fault. 
No  work  has  been  done  in  the  Fox  crosscut  since  the  fall  of  1923. 


—  135  — 

GARFORD   LEASE. 

The  Garford  Lease  Shaft,  hioated  500  feet  southeast  of  tlic  Bfk-her 
Extension  Shaft,  near  the'  southern  termination  of  the  outcrop  of  the 
Footwall  Vein,  is  developed  by  a  vertical,  li-compartment  shaft,  300 
feet  deep.  Levels  are  run  at  85,  200  and  300  ftn-t.  On  the  S^)  foot  level 
is  a  150  foot  crosscut  to  the  southeast.  On  the  200  foot  level  a  crosscut 
has  been  run  300  feet  northwest  to  the  Footwall  Vein,  and  drifts  300 
feet  to  the  nortlieast  and  150  feet  to  the  southwest  alon^  the  vein.  The 
Footwall  Vein  here  carries  very  spotted  values  in  ^rold  and  silver. 
Gold  assays  of  $6.00  to  $7.(X)  and  silver  assays  a,s  high  as  180.  oz.  of 
silver  per  ton  have  been  obtained  from  picked  samples.  The  chief  silver 
values  were  obtained  from  a  gouge  streak  two  inches  Ande  which  was 
traced  for  200  feet  along  the  strike  of  and  within  the  Footwall  Vein. 

On  the  300  foot  level  the  Footwall  Vein  was  entered  200  feet  north- 
west from  the  shaft.  The  Footwall  Vein  here  consists  of  a  brecciated 
zone  of  silicified  schist,  containing  a])undant  pyrite,  which  is  75  feet 
thick,  incasuivnl  horizontally.  Numerous  vugs  occur  in  the  vein.  Neither 
the  footwall  nor  the  hanging  wall  are  well  defined. 

The  Garford  Lease  was  relintiuished  by  its  holders  in  July,  1923,  and 
has  since  been  taken  over  under  a  working  agreement  by  the  ^lonarch 
Rand  ^Mining  Company. 

HARD  TACK. 

The  Hard  Tack  property,  worked  l)y  the  Hard  Tack  ]\Iining  Com- 
pany, lies  approximately  2  miles  northwest  of  Johannesburg.  The 
]iropei'ty  is  developed  ])y  a  vertical  shaft,  135  feet  deep,  and  l)y  350  feet 
of  drifts  along  a  level  at  a  depth  of  105  feet.  This  work  has  l)een  carried 
out  in  the  hope  of  picking  up  an  old  vein  from  which  a  small  produc- 
tion is  reported  to  have  been  made  in  past  years.  A  number  of  old 
workings  exist  on  the  property. 

HUMMER. 

The  Hummer  property,  formerly  known  as  the  JoUiver,  consists  of 
seven  claims  located  in  the  El  Paso  ^Mountains  just  south  of  El  Paso 
Peaks.  The  property  was  first  worked  in  1851.  according  to  old  location 
notices  found  on  the  property,  and  has  been  relocated  three  times  since 
— the  last  time  in  1919. 

The  property  is  developed  by  an  incline  shaft  114  feet  deep,  and 
short  drifts  at  34,  54  and  114  feet.  The  workings  follow  a  thin  vein 
from  which  several  small  bunches  of  ore  have  been  mined.  Approxi- 
mately 24  tons  of  ore  having  a  gross  value  of  about  $2000  have  been 
shipped  from  the  property  in  past  years.  The  values  are  chieflj^  in  the 
form  of  argentiferous  galena,  though  some  gold  is  present  in  the  ore. 


JULIUS  SHADES. 


This  property  consists  of  a  lease  on  seven  and  a  fraction  claims, 
located  approximately  a  mile  north  of  Randsburg.  A  number  of  old 
workings  exist  on  the  property  to  which  some  new  work  has  been  added. 
These  include  an  incline  shaft  along  a  vein  which  strikes  N.  10^  E., 
dipping  65°  E.,  and  some  drifting  along  the'  vein. 


—  136  — 

Another  shaft  of  low  inclination  has  been  sunk  on  another  vein 
further  east  and  a  certain  amount  of  drifting  carried  on.  The  vein 
consists  wholly  of  iron-stained  schist  practically  free  from  vein  quartz. 
Xo  ore  had  been  discovered  up  to  the  time  of  the  writer's  visit,  altliough 
the  property  is  credited  with  a  small  production  a  number  of  years  ago. 

The  property  is  equipped  with  a  light  10-stanip  mill  recently 
erected.  The  writer  understands  that  this  mill  is  now  operating  on 
ore  discovered  since  his  visit. 

KELLY    RAND    EXTENSION. 

The  shaft  of  the  Kelly  Rand  Extension  ^Mining  Company  lies  about 
]500  feet  north  of  west  from  the  California  Rand  No.  1  shaft.  The 
.shaft  is  1^  compartment,  vertical,  and  625  feet  deep.  The  only  lateral 
work  consists  of  80  feet  of  crosscuts  on  the  600-foot  level.  Xo  veins  were 
found.  The  property  was  closed  down  early  in  1923.  It  is  under- 
stood that  further  work  was  being  undertaken  in  the  fall  of  1923. 

KING   SOLOMON. 

The  King  Solomon  ^line,  comprising  five  and  a  fraction  claims,  is 
owned  by  the  Xorth  Rand  Silver  ^Mining  Company.  The  property, 
located  just  southwest  of  Johannesburg,  is  developed  by  several  shafts, 
the  main  shaft  being  2  compartments,  inclined,  and  480  feet  deep 
measured  on  tlie  incline. 

There  are  seven  mine  levels,  the  deepest  being  -ISO  feet,  and  approxi- 
mately 9000  feet  of  workings.     Three  winzes  extend  below  the  480  level. 

A  nundier  of  veins  have  been  worked  in  the  property.  The  King 
Solomon  Vein  strikes  S.  80°  E.,  dippinu"  40°  N.  It  averages  from  2 
to  4  feet  in  width.  The  :\Iain  Vein  strikes  X.  35°  W.,  dipping  45°  XE., 
and  averaging  2  feet  in  width.  A  cross  vein,  1^  feet  thick,  is  now 
l^ing  worked  south  of  the  .shaft.  It  strikes  S.  70°  E.,  and  dips  50°  N. 
This  vein  intersects  the  ]\Iain  Vein  south  of  the  shaft. 

The  veins  are  in  general  badly  l)recciated  and  consist  chiefly  of 
mineralized  and  iron-stained  schist  with  some  vein  quartz.  The  walls 
of  the  veins  are  usually  sharply  defined,  being  strongly  slickensided 
and  lined  with  gouge.  Ordinarily  tlie  hanging  wall  is  better  defined 
than  the  footwall. 

The  wall  rocks  are  in  places  schist,  in  other  places  quartz  monzonite. 
Occasionally  the  schist  and  quartz  monzonite  appear  opposite  each 
other  on  the  two  walls  of  the  same  vein.  The  cro.ss  vein  mentioned 
above  in  places  cuts  through  a  large  and  irregidar  diabase  dike.  The 
diabase  locally  is  .strongly  mineralized.  The  vein  narrows  where  it 
l)asses  through  the  dike. 

The  values  in  the  veins  are  quite  eTratic.  In  general  they  cling  close 
to  the  hanging  wall  of  the  veins  in  connected  but  more  or  less  irregular 
bunches.  The  best  ore  which  has  been  mined  occurred  ad.iacent  to 
the  main  shaft  between  the  300  level  and  the  .surface. 

The  present  daily  mine  production  is  about  five  tons,  or  enough  to 
keep  the  5-stamp  amalgamation  mill  operating  one  shift  each  day. 
Xo  concentrators  are  used  in  the  mill  since  the  ore  contains  almost  no 
sulphides,  being  completely  oxidized  and  free  milling. 

The  average  grade  of  the  ore  mined  is  such  that  approximately  $25.00 
is  caught  on  the  plates  for  each  ton   milled.     The  gold  produced  is 


—  137  — 

wortli    al)0iit   .i^l").0()   ;ni   oiiiieo   acr-nrdiiiir  to   tln'   iniiio   siiporintendcnt. 
-Mine  returns  iiulicate  a  liiu'iu'ss  of  at)()Ut  7S(). 

The  total  i)roduetion  of  the  property  is  not  definitely  known  dui^  to 
the  methods  of  keeping  accounts  in  the  early  life  of  the  property,  but 
it  is  estimated  to  be  between  $.3()0,()00  and  !|<5()( ),()()().  The  production 
for  the  three  months  ending'  July  li),  11)2:5,  amounted  to  G.lD.o  ounces  of 
gold. 

LITTLE  BUTTE. 

The  Little  Butte  ]\Iine,  owned  by  the  Little  Butte  ^Mining  and  ^Milling 
Company,  is  located  across  the  gulch  just  north  of  Rnndsburg.  The 
property  is  developed  by  a  single  compartment  incline  shaft  600  feet 
deep,  as  measured  on  the  incline,  and  by  1800  feet  of  drifts,  distributed 
among  nine  levels. 

Two  veins  are  worked  in  the  property.  These  strike  noi'thwest  and 
dip  -15  XE.  These  veins  are  known  to  cut  tiirougli  i-hyolite  dikes  in 
the  mine.  One  of  the  veins  lies  on  the  footwall  of  a  small  diabase  dike. 
With  these  exceptions  the  wall  rocks  are  .schist.  The  hanging  walls  of 
the  veins  are  well  defined. 

Ore  possessing  a  value  of  $600  per  ton  has  been  mined  from  one  of 
the  veins.  The  other  vein  has  locally  given  assays  of  $250  in  gold  and 
10  ounces  of  silver  per  ton  across  a  width  of  3^  feet.  The  vein  matter 
consists  of  brecciated  schist,  badly  iron-stained,  cut  by  quartz  stringers. 
Tlu^  values  are  very  spotted.  All  of  the  ore  mined  has  been  oxidized 
and  free  milling.  The  ore  on  the  600  level  is  sulphide  ore.  It  is  said  to 
assay  from  $6.00  to  $25.00  in  gold  and  3  to  4  ounces  of  silver  per  ton. 
The  gross  production  of  the  property  is  estimated  to  have  be(>n  $400,000. 

The  mine  has  been  shut  down  since  January  12,  1!)23.  At  present 
water  stands  at  500  feet  in  the  shaft.  It  is  stated  that  previous  to  the 
San  Francisco  earthquake  in  1906,  no  water  existed  at  a  depth  of  520 
feet,  but  appeared  at  tlie  time  of  tlie  earthquake. 

The  mine  is  equipped  with  a  2-stamp  mill  consisting  of  950-pound 
stamps. 

The  Kenj'on  and  Wedge  properties  adjoin  the  Little  Butte  on  the 
southeast,  working  file  same  veins.  The  Kenyon  property  is  opened 
by  a  400-foot  incline  shaft ;  the  Wedge  by  a  vertical,  single-compartment 
shaft.  Neither  property  has  been  recently  operated.  Their  combined 
production  is  estimated  to  have  been  $500,000. 


MINNEHAHA. 

The  four  claims  composing  tiie  ^linnehaha  property  lie  to  the  west 
of  the  Yellow  Aster  holdings.  The  property  has  been  worked  inter- 
mittently for  the  last  25  years,  having  been  located  in  July,  1895.  The 
mining  has  been  done  entirely  by  leasers. 

There  are  over  1000  feet  of  workings  on  the  property,  the  deepest 
development  being  300  feet.  Most  of  tlie  work  has  been  done  on  a  vein 
which  strikes  N.  35°  AV.,  and  dips  45°  NE.  The  vein  is  lenticular  in 
hal)it,  locally  being  7  or  8  feet  wide.  The  wall  rocks  are  chiefly  schist, 
with  some  quartz  monzonite,  though  locally  the  vein  cuts  rhyolite  or 
([uartz  latite  dikes. 

The  values  in  the  vein  are  extremely  spotted  and  erratic,  some  of 
the  ore  mined  showing  a  value  of  $120  per  ton.  The  ore  has  been 
milled  in  various  mills  of  the  district,  tlie  latest  shipment  being  late 


—  138  — 

in  1922.     The  total  production  of  the  property  is  estimated  to  have 
been  $100,000. 

MIZPAH    MONTANA. 

This  property,  comprising  two  fractional  claims  owned  by  the  Mizpah 
Montana  jMining  Company,  Inc.,  lies  1500  feet  northwest  from  the 
California  Rand  No.  1  Shaft.  The  property  is  developed  by  a  2-com- 
partment,  vertical  shaft  700  feet  deep,  and  by  approximately  1300  feet 
of  horizontal  workings  distributed  among  seven  levels.  The  level 
interval  is  100  feet.  No  work  has  been  done  on  the  300  and  600  foot 
levels  aside  from  cutting  stations.  The  worlvings  are  partly  in  quartz 
monzonite  and  partly  in  schist,  being  located  near  the  intrusive  contact 
l)et^veen  these  two  groups  of  rocks. 

Two  small  bunches  of  ore  were  removed  from  a  series  of  veinlets 
near  the  shaft  station  on  the  100-foot  level.  The  veinlets  formed  a 
small  stockwork  in  tlu^  quartz  monzonite,  striking  from  north  to  N. 
40°  E.,  and  varying  in  dip  from  vertical  to  40^  E.  Some  of  the  vein- 
lets  were  2  inelies  thick.  The  silver  minerals  identified  as  being  present 
were  cerargyrite  and  miargyrite.  Approximately  12  to  15  tons  of  ore 
were  mined  which  were  said  to  average  $20.00  in  gold  and  about  100 
ounces  in  silver  per  ton. 

On  the  500  level  a  vein  was  encountered  60  feet  south  of  the  shaft 
which  possessed  a  strike  of  N.  40°  E.,  dipping  65°  SE.  This  vein  was 
picked  up  again  northeast  of  the  shaft.  To  the  south  of  the  shaft  it 
varies  frdm  4  to  10  feet  in  widtli  and  gives  average  assays  of  $7.00  to 
$9.00.  Of  this  from  3  to  5  ounces  is  silver.  Some  cossays  as  high 
as  $34.00,  chiefly  gold,  have  been  obtained.  The  vein  matter  is  a  dark 
gray  siliceous  filling,  more  or  less  breceiated  and  containing  numerous 
schist  fragments.  Pyrite  and  stibnite  are  abundant.  The  wall  rocks 
are  sehist,  though  locally  diabase  occurs  on  this  level.  The  latest  pros- 
pecting work  in  the  mine  is  being  carried  on  northeast  of  the  shaft  on 
the  7th  level  along  what  is  probably  a  continuation  of  this  vein. 

MIZPAH    NEVADA. 

This  property,  composing  a  fractional  claim  and  an  option  on  two 
adjoining  claims,  lies  1200  feet  northwest  of  the  ^Mizpah  IMontana. 
It  is  owned  by  the  IMizpah  Nevada  IMining  Company,  Inc. 

The  property  is  developed  by  a  1^-compartment  vertical  shaft,  150 
feet  deep,  and  a  40-foot  crosscut  to  the  south.  All  the  workings  are  in 
([uartz  monzonite,  A  small  irregular  diabase  dike  is  exposed  at  the 
bottom  of  the  shaft.     Work  on  the  property  has  been  discontinued. 

MONARCH    RAND. 

The  original  workings  of  the  Monarch  Rand  Mining  Company  were 
aiiproximatoly  1600  feet  southeast  of  tlie  Baltic  Shaft.  The  Monarch 
Rand  Shaft,  now  known  as  the  Monarch  No.  1,  is  a  1-J-compartment 
vertical  shaft,  now  450  feet  deep.  It  is  planned  to  sink  to  700  feet. 
Stations  have  been  cut  at  118,  168  and  218  feet.  One  vein,  3^  feet  thick, 
has  been  found  in  this  shaft  which  was  said  to  assay  $48.00,  chiefly  in 
gold.  Tliis  vein  which  lays  on  the  hanging  wall  of  a  quartz  latite  dike, 
was  cut  off  on  top,  bottom  and  both  ends  by  faults.  100  tons  of  ore 
were  taken  from  the  No.  1  shaft. 


—  139  — 

The  Monarch  Rand  ]\Iiuinpr  Company  have  recently  ac-qnired  the 
Baltic  claim,  including  the  old  mine  and  mill,  and  also  the  property 
formerly  known  as  the  l^cn  Iliir  Extension. 

It  is  understood  that  a  working  agreement  has  been  reached  whereby 
the  ^Monarch  Rand  property  will  be  explored  by  a  crosscut  driven  from 
the  300-foot  level  of  the  Garford  Lease  Shaft. 

NANCY   HANKS. 

During  the  sununer  of  1923  the  Xancy  Hanks  Mine  belonging  to  the 
Yellow  Aster  Mining  and  ^Milling  Company  was  under  lease  to  the 
Belcher  Extension  ]\Iining  Company.  The  property  is  developed  by  a 
shaft  190  feet  deep,  and  three  levels  along  a  vein  striking  N.  70°  E.,  and 
dipping  45°  NW.  The  vein  varies  from  1  to  7  feet  in  Avidth.  It 
possesses  a  well-defined  hanging  and  poorly -defined  footwall.  The  wall 
rocks  are  schist.  A  second  narrow  vein  occurs  in  the  footwall.  The 
vein  matter  consists  of  iron-stained  schist  with  very  little  quartz.  Some 
of  the  ore  assays  .$30.00  across  two  feet  of  the  vein. 

During  the  summer  of  1923,  the  ore  being  mined  as  well  as  screen- 
ings from  the  old  stopes  w^ere  being  milled  in  the  Baltic  mill. 

NAVAJO   AND   SWASTIKA. 

The  Navajo  and  Swastika  shafts  are  locally  called  the  Grady  No.  2 
and  No.  1  shafts,  respectively.  The  Swastika  Shaft  was  in  alluviuT-i 
and  the  Rosamond  formation  to  a  deptli  of  497  feet  when  tlie  schist 
was  entered. 

The  Navajo  Shaft,  2-compartment  and  vertical,  passed  through  670 
feet  of  Rosamond  sandstones  before  entering  the  schist.  The  shaft  is 
1130  feet  deep,  levels  ])eing  cut  at  800  feet  (8th  level)  and  975  feet 
(10th  level).  No  veins  were  encountered  on  the  10th  level,  the  schist 
being  blocky  and  in  general  unaltered.  On  the  8th  level  a  vein  was 
encountered  about  200  feet  northwest  of  the  shaft.  This  vein  strikes 
ai)proximately  N.  25°  E.,  dipping  40°  SE.  Its  width  varies  from  2  to 
10  feet,  and  throughout  it  assays  from  2  to  10  ounces  of  silver  per  ton, 
with  locally  much  higher  values.  The  vein  is  more  or  less  brecciated 
and  possesses  Avell-defined  walls,  striated  and  lined  with  gouge. 

A  drift  has  been  run  along  this  vein  for  1050  feet  to  the  north.  A 
small  offset  occurs  at  550  feet  north  of  where  the  vein  was  first  encoun- 
tered.    North  of  this  offset  the  vein  maintains  a  course  of  N.  10°  W. 

Preparations  were  being  made  to  discontinue  operations  in  January, 
1924. 

ONEY   LEASE. 

The  Oney  Lease  is  located  about  800  feet  west  of  the  Garford  Lease. 
The  property  is  developed  by  a  shaft  200  feet  deep.  The  workings 
follow  a  vein  striking  northwest  and  standing  vertical.  The  vein  is 
composed  largely  of  quartz,  l)eing  about  3  feet  thick.  It  is  exposed  on 
the  150-foot  level  for  20  feet.  The  vein  as  a  Avhole  where  exposed  on 
the  150-foot  level  is  said  to  assay  from  $50  to  $75  per  ton,  but  in  the 
center  of  the  vein  is  a  streak  of  high  grade  ore  which  is  said  to  run 
as  high  as  $2600  per  ton.  Locally  this  streak  is  6  inches  wide.  EtTorts 
are  now  being  made  to  cut  this  ore  shoot  on  the  200-foot  level. 


—  140  — 

OPERATOR    DIVIDE. 

During  1923  the  Operator  Divide  Mining  Company  took  over  a  group 
of  7  claims,  including  the  old  Phoenix  ]\Iine,  and  located  just  north 
of  Johannesburg. 

Five  known  veins  cross  the  property,  the  two  principal  ones  having 
been  worked  in  the  Phoenix  Mine.  The  veins  strike  nortliAvest  and  dip 
21°  NE.  They  vary  from  mere  stringers  up  to  thicknesses  of  possibly 
7  feet,  being  lenticular  in  liabit.  The  average  width  would  ])e  between 
2  ami  3  feet.  The  wall  rocks  are  chiefly  schist,  thoujih  in  many 
places,  rhyolite  or  diabase  dikes  occur  as  vein  walls.  Some  of  these  dikes 
are  quite  large,  and  in  some  cases  they  carry  traces  of  gold  and  silver. 

The  veins  have  well-developed  hanging  walls,  which  connnonly  show 
gouge  and  striations.     The  veins  commonly  grade  into  the  footwall. 

The  vein  matter  consists  almost  entirely  of  iron-stained  schist  cut 
by  occasional  small  quartz  stringers.  The  ore  is  entirely  oxidized  and 
free  milling,  the  gold  contained  by  it  being  quite  fine.  Tlie  ore  mined 
in  i)ast  years  probably  had  a  value  varj'ing  from  a  few  dollars  up  to 
$35.00  per  ton. 

The  Phoenix  ]\line  is  developed  by  an  incline  shaft  300  feet  deep, 
and  by  over  2000  feet  of  workings  distributed  through  6  levels.  Two 
of  these  levels  were  driven  from  a  winze  which  extends  100  feet  below 
the  bottom  of  the  shaft. 

The  mine  was  equipped  with  a  5-stamp  mill  when  taken  over  by 
the  Operator  Divide  ^Mining  Oompany.  This  has  lieen  remodeled  and 
5  new  stamps  added,  making  10  in  all. 

The  Phoenix  Mine  is  credited  with  a  production  in  past  years  of 
about  $600,000.  Over  35,000  tons  of  ore  were  milled,  giving  an  average 
value  for  all  the  ore  mined  of  about  $17.00  per  ton. 

After  operating  for  a  short  time  during  the  fall  of  1923  the  property 
was  again  closed  down. 

RAND   CONTACT. 

The  Rand  Contact  Silver  (xi-oup  is  composed  of  five  claims  located 
south  of  the  Black  Hawk  ]\Iine  near  the  contact  between  the  quartz 
monzonite  and  the  schist.  The  property  is  developed  b,y  a  vertical 
shaft,  100  feet  deep,  and  a  drift  south  for  120  feet,  run  in  an  effort  to 
intersect  the  contact.  Work  was  suspended  before  the  contact  was 
readied. 

RAND    MOUNTAIN. 

The  Rand  Mountain  Group,  composed  of  six  claims  lying  northeast 
of  the  Navajo  shaft,  is  operated  by  the  Rand  ^Mountain  Silver  IMining 
Company,  Inc.  The  developments  consist  of  a  l|-compartment  vertical 
shaft  435  feet  deep.  The  shaft  is  entirely  in  the  Rosamond  Forma- 
tion.   Xo  work  has  been  done  on  this  property  since  the  fall  of  1923. 

RANDSBURG  ASSOCIATED  MINES,  INC. 

The  Randsburg  Associated  Mines  Company  holds  four  groups  of 
claims,  namely,  the  North  Rand  and  ]\[yra  Queen  Groups  (240  acres) 
iu)rth  of  Red  Mountain ;  the  Silver  Queen  Group  composed  of  three 
fractional  claims  lying  between  tlie  Flat  Tire  and  Big  Four  shafts ; 
and  the  Commonwealth  Group  of  two  claims,  l.ving  a  half  mile  to  the 
nortlieast  of  the  Silver  Queen  Group. 


—  141  — 

Developments  on  tlie  Xortli  Rand  and  M\  rn  Queen  trroups  include 
a  4()()-t'oot  iueline  sliat't,  a  KiS-i'oot  vei'tit-ai  shaft,  and  a])jM-()xiniat<'ly 
14(>(t  feet  of  drifts  and  crosscuts.  l)esides  a  number  of  shallow  shafts 
and  tunnels.  A  number  of  mineralized  stringers  and  veinlets  have 
l»('i  II  discovered,  but  none  of  commercial  importance. 

X(t  woi-k,  othei'  than  that  r('((uire(|  l)y  ];i\v  luis  been  done  on  the 
( 'oiiiinoiiwcallh  (ii'oui). 

A  new  shaft,  located  attout  inidwjiy  lictwcfii  the  Ui^-  Four  and  Mat 
Tire  shafts  was  started  on  the  Silver  Queen  Group  late  in  J 923.  In 
January,  1924,  this  shaft  was  down  40  feet.  It  is  vertical  and  has  1^ 
compartments.  Probably  lOUO  feet  of  the  Rosamond  formation  must  be 
penetrated  before  the  shaft  will  enter  the  quartz  monzonite. 

SILVER    BASIN. 

The  Silver  Hasin  property,  coinpi'isiiin-  five  elaims  totaling'  al)out 
60  acres  lies  to  the  southeast  of  Ihi'  Black  Hawk  ]\line.  The  j)ro])erty 
is  owned  by  the  Silver  Basin  Mining  Company,  Inc.  A  rich  gold  dis- 
cover}' was  made  on  the  property  July  I).  1923,  a  vein  being  found 
wliich  panned  coarse  tiold  and  gave  assays  varying  from  -tSLOO  to 
$432.00  })er  ton  across  a  width  of  two  feet. 

E(iuipnient  was  installed  and  an  incline  shaft  100  feet  deep  sunk 
along  the  vein.  The  vein  in  depth  rapidly  degenerated  into  a  mere 
strinuci',  which,  liowever,  continued  to  ]ian  gold.  About  500  feet  of 
horizontal  work  has  been  carried  0!i  without,  as  yet,  any  new  discoveries 
having  been  made. 

The  vein  at  the  surface  had  a  strike  of  N.  85°  E.  It  consisted  of  iron- 
stained  schist  with  occasional  (piartz  veinh^ts  cutting  it.  The  wall 
rocks  were  schi.st. 

SILVER    BELL. 

The  Silver  Bell  Mining  Company  holds  a  group  of  three  claims 
adjoining  the  California  Rand  Silver  holdings  on  the  west.  The 
pi'operty  is  developed  by  a  1  ^-compartment  vei'tical  shaft  702  feet  in 
depth,  and  by  .slightly  over  700  fet't  of  drifting  divided  between  levels 
at  oiK)  feet  and  700  feet.    All  of  the  w^orkings  are  in  schist. 

On  the  500-foot  level  four  veins  were  cut  within  200  feet  of  the  shaft. 
Eacli  possessed  a  strike  of  N.  40°  E.,  dipping  40"^  SE.  In  order  from 
the  shaft,  the  veins  are  3,  14,  3  and  3  feet  thick,  respectively.  Each 
vein  was  composed  of  gray  siliceous  gangue,  somewhat  brecciated,  and 
showing  open  drusy  cavities  and  some  pyrite. 

On  the  700-foot  level,  a  vein  4  feet  thick  was  cut  90  feet  east  of 
the  shaft.  This  was  probably  one  of  the  veins  cnconnlejed  on  the  500- 
foot  level.    Four  other  smaller  veins  occur  within  the  next  90  feet  ea.st. 

SILVER   GIANT. 

The  Silver  Giant  Miiung  C^onipany  liolds  a  group  of  four  mining 
claims  situated  well  up  on  the  northwest  slope  of  Red  Mountain.  The 
center  of  the  property  is  almost  2'  miles  northeast  of  the  No.  1  Shaft 
of  the  California  Rand  Silver  Mine.  The  development  on  the  property 
consists  of  a  14-compartment  shaft  down  only  80  feet,  all  in  the  Rosa- 
mond formation.  The  entire  area  covered  l)y  the  Silver  Giant  group  is 
underlain  by  the  Rosamond  formation.  (Some  lavas  may  occur.)  No 
attempt  was  made  to  determine  its  thickness  here,  but  probably  several 


—  142  — 

hundred  feet  of  strata  at  least  must  be  passed  through  before  the  under- 
lying rocks,  probably  quartz  nionzonite,  will  be  reached. 

SILVER   GLANCE   LEASE. 

The  Silver  (4 lance  Lease,  working  on  property  owned  by  the  Johan- 
nesburg Mining  and  Milling  Company,  is  being  developed  by  a  1^- 
compartiuent  vertical  shaft.  This  shaft  is  located  about  600  feet  south- 
east of  the  Silver  King  Shaft.  It  has  only  recently  (April,  1924), 
passed  througli  the  Rasaniond  formation  into  the  underlying  Rand 
sehist,  reaehing  the  schist  at  a  depth  of  502  feet. 

SILVER   KING. 

The  Silver  King  and  Silver  Moon  properties  are  owned  by  the  Johan- 
nesburg ]\Iining  and  Milling  Company.  The  Silver  King  property 
is  developed  by  a  1^-eompartment  vertical  shaft,  slightly  over  700  feet 
deep.  The  upper  469  feet  passed  through  Rosamond  strata.  Below 
469  feet  the  shaft  is  in  schist.  A  number  of  small  dikes  of  rhyolite  are 
reported  as  having  been  cut  in  passing  through  the  lower  200  feet  of  the 
Rosamond  series. 

The  schist  encountered  in  the  shaft  is  for  the  most  part  badly  broken 
and  altered,  being  cut  by  calcite  stringers  and  containing  scattered 
crystals  of  pyrite  and  stibnite. 

The  first  vein,  3  feet  thick,  was  encountered  at  a  depth  of  603  feet, 
and  dipped  to  the  east  at  an  angle  of  18°.  Over  a  width  of  1 
foot  this  vein  gave  assays  of  from  600  to  900  oz.  of  silver.  Two  ship- 
ments of  ore  were  made  from  this  vein,  one  of  38^  tons,  the  other  of  34f 
tons.  The  shipments  returned  $5.80  in  gold  and  93  oz.  of  silver,  and 
$8.80  in  gold  and  98  oz.  of  silver,  respectively. 

A  drift  was  run  140  feet  east  of  the  shaft  on  the.  600  foot  level. 

The  next  drifting  was  done  on  the  650-foot  level,  where  205  feet  of 
openings  were  run.  This  drifting  was  along  a  vein  striking  N.  38^"  E. 
Good  ore  was  obtained  near  the  shaft  and  also  90  feet  south  of  the 
shaft  where  the  northeast  vein  was  cut  off  by  a  north-south  vein. 

Six  hundred  feet  of  work  has  been  done  on  the  700-ioot  level.  A 
vein  striking  north  was  encountered  40  feet  from  the  shaft.  This  vein 
which  is  7  feet  wide  dips  from  62°  to  65°  east,  and  gives  assays  of 
from  9  to  20  oz.  of  silver  per  ton  across  5  feet. 

Two  veins  split  off  from  this  north-south  vein,  one  40  feet  from 
the  shaft,  the  other  115  feet  north.  These  veins  strike  about  N.  30°  E., 
dipping  65°  and  76°  SE.  The  first  of  these  veins  locally  assays  26.2  oz. 
of  silver  across  3  feet. 

The  Silver  Moon  property  lies  to  the  south  of  the  Mizpah  Montana 
Shaft.  It  is  developed  by  a  vertical  shaft  550  feet  deep.  Levels  are 
cut  at  200,  300  and  550  feet.  Over  100  feet  of  work  was  done 
on  the  200-foot  level,  several  narrow  veins  being  prospected.  There 
are  323  feet  of  workings  on  the  300-foot  level.  One  vein,  22  feet  thick, 
was  cut  103  feet  ea.st  of  the  shaft.  This  vein  strikes  N.  40°  E.,  dipping 
35°  E.     The  vein  here  carried  only  traces  of  silver. 

Approximately  850  feet  of  work  was  done  on  the  550-foot  level.  The 
vein  encountered  on  the  300-foot  level  was  found  269  feet  east  of  the 
shaft  and  thoroughly  prospected.  It  here  carried  up  to  4.4  oz.  of 
silver  and  $4.00  in  gold  per  ton. 


—  143  — 


SILVERTON. 


The  Silverton  property,  composing  eleven  and  a  fraction  claims,  is 
located  somewhat  over  2  miles  south-west  of  the  Rand  Contact  Group. 
Tt  is  operated  by  the  Silverton  .Mining  Company.  The  property  is 
developed  by  an  inclined  shaft,  160  feet  deep,  and  a  40-foot  crosscut  on 
the  lOO-foot  level.  The  shaft  follows  down  the  footwall  of  a  fracture 
striking  X.  70^  E..  and  dipping  75°  S.  The  gouge  from  this  fracture 
assays  2  ozs.  of  silver  and  about  $6.00  per  ton.  No  other  veins  have 
been  found. 

SOUTH    RAND. 

The  South  Rand  Alining  Company  holds  100  acres  of  ground  about 
a  un\o  nortli  of  the  Silverton  holdings.  There  are  three  shallow  shafts 
on  the  property.  A  new  shaft  was  started  July  1,  1923,  but  after 
reaeliing  a  depth  of  90  feet  work  was  suspended.  The  work  done 
has  been  along  a  vein  striking  east  and  dipping  75°  S.  A  second 
parallel  vein  occurs  80  feet  to  the  north.  The  wall  rocks  are  schist 
and  a  number  of  quartz  latite  dikes. 

ST.  LAWRENCE  RAND. 

The  St.  La\\Tence  Rand  Mining  Company  holds  a  lease  from  the 
California  Rand  Silver  Mining  Company  on  portions  of  nine  claims, 
known  as  the  K.  C.  X.  Group,  located  approximately  4000  feet  west 
of  the  California  Rand  Silver  Mine. 

The  property  is  developed  by  a  number  of  old  workings,  and  in  addi- 
tion an  inclined  shaft  450  feet  deep.  Levels  are  cut  at  100  feet  (240 
feet  of  drifting)  ;  250  feet  (772  feet  of  drifting)  ;  350  feet  (182  feet 
of  drifting)  ;  and  450  feet  (242  feet  of  drifting),  or  a  total  of  1436  feet 
of  drifting  to  January  1,  1924. 

The  new  workings  are  along  a  single  inclined  vein  which  strikes 
X.  62"  E..  and  dips  67°  S.  The  vein  pinches  and  swells  from  a  few 
inches  to  as  much  as  7  feet.  It  carries  silver  values  throughout, 
which,  however,  are  very  erratic.  The  vein  usually  possesses  Avell- 
defined  walls  which  show  a  .strong  development  of  gouge  and  slicken- 
siding.  The  vein  matter  is  a  gray  siliceous  material,  locally  brecciated 
and  containing  pyrite,  stibnite  and  miargyrite.  The  limit  of  oxidation 
in  general  appears  to  be  about  250  feet  as  measured  down  the  dip  of 
the  vein. 

The  wall  rocks  are  chiefly  schist,  though  in  the  shaft  near  the  250- 
foot  level,  and  on  the  450-foot  level  west  of  the  shaft,  diabase  which 
is  itself  mineralized  serves  as  a  wall  rock. 

AVhile  much  of  the  vein  carries  only  a  few  ounces  of  silver  per  ton, 
occasional  portions  of  the  vein  arc  much  higher  in  their  content  of 
silver.  One  lot  of  6100  lbs.  of  ore  was  removed  from  the  250-foot 
level  which  averaged  $75.00  per  ton. 

TREASURE   HILL. 

The  Treasure  Hill  Mining  Company,  Inc.,  is  operating  a  group  of 
three  claims  lying  1200  feet  to  the  east  of  the  St.  Lawrence  Rand 
property.  The  property  is  developed  by  a  2-compartment  vertical 
shaft  which  was  540  feet  in  depth  in  January.  1924,  sinking  operations 
being  still  in  progress.     A  small  amount  of  horizontal  work  has  been 


—  144  — 

(loue  on  levels  at  400  feet  and  500  feet.     All  of  the  workings  are  in 
schist. 

A  vein  Avas  cut  in  the  shaft  at  a  depth  of  400  feet.  It  was  8  feet  thick 
where  it  crossed  the  shaft,  and  possessed  a  strike  of  N.  60°  E.,  dipping 
72°  SE.  This  appears  to  be  a  continnation  of  the  vein  being  worked 
in  the  St.  Lawrence  Rand  property.  The  vein  matter  varies  from  a 
dark  gray  siliceous  fine-grained  material  to  white  quartz.  It  carries 
some  sulphides,  chiefly  pyrite.  The  vein  has  strong  walls  and  is  some- 
what breceiated.  Good  gold  assays  are  said  to  be  obtained  locally  from 
the  vein. 

WHITE   HORSE   RAND. 

The  White  Horse  Rand  Mining  Company  holds  11  acres  near  the 
highway  southeast  of  the  St.  Lawrence  Rand  holdings.  The  property 
is  being  prospected  by  means  of  a  1^-compartment  vertical  shaft  which 
is  about  200  feet  deep.  Several  small  flat  veins  or  stringers  of 
quartz  were  cut  in  siidiing  the  shaft.  No  lateral  work  has  been  done. 
Work  was  discontinued  in  the  summer  of  1923. 

OTHER   LODE    PROPERTIES. 

A  large  n\unl)er  of  properties  exist  in  the  region  about  Randsburg 
which  have  not  been  worked  for  many  years,  or  which  were  not  operat- 
ing at  the  time  of  the  writer's  visit,  and  about  which  little  information 
was  available. 

Among  the  more  recent  workings  (chiefly  silver  prospects)  which  the 
writer  was  unable  to  visit  may  be  mentioned  the  Gimlet,  Ij'ing  3000 
feet  west  of  the  Black  Hawk  IMiiu^;  the  Good  Morning,  lying  3500  feet 
east  of  the  Silver  Basin ;  the  Grady  Extension  and  the  Little  Jack,  east 
and  southeast  of  the  Navajo  shaft;  the  Joburg  Divide,  just  east  of 
Johannesburg;  and  the  Mojave  Rand,  northeast  of  Red  ^lountain. 
Several  of  these  properties  are  developed  only  by  shafts,  without  any 
lateral  work. 

Among  the  properties  which  made  some  tungsten  production  during 
the  war  which  were  not  visited  are  the  Osdick  property  east  of  Atolia, 
reported  to  have  produced  tungsten  worth  $157,000,  the  Ratcliffe 
property  and  the  Jersey  Lily,  north  of  the  Black  Hawk  Mine. 

j\iany  older  properties  exist  which  have  made  some  little  production 
in  past  years,  the  details  of  which  have  in  many  cases  been  forgotten. 
Prominent  among  these  are  the  Sunshine,  La  Crosse  and  Winnie,  the 
former  of  which  produced  $1,060,000  in  gold  from  a  narrow  quartz  vein 
striking  east  and  standing  vertical.  The  property  was  worked  to  a 
depth  of  600  feet. 

Adjoining  the  old  Phoenix,  now  the  Operator  Divide,  on  the  west 
is  the  Pinmore,  and  on  the  east  the  Alameda,  each  with  a  past  produc- 
tion record.  The  Gold  Coin,  on  th(>  property  now  held  by  the  Monarch 
Rand  Mining  Company,  is  an  old  protlucer,  while  south  of  Atolia  is  the 
St.  Elmo  from  which  some  ore  has  been  taken  recently.  Other  mines 
which  might  be  mentioned  and  which  are  now  inaccessible  are  the 
Napoleon,  whieh  produced  over  $10(),0(K1,  and  the  Gold  Bug. 

PLACER    DEPOSITS. 

The  original   gold   discovery   in   the   quadrangle  was  made   in   the 
placer  deposits  in  the  vicinity  of  Summit  Diggings.    Some  small  produc- 


—  145  — 

tion  has  come  from  these  deposits  practically  every  year  since.  Gold 
placers  were  also  at  one  time  worked  on  the  north  slope  of  the  Rand 
-Aronntains,  but  those  were  ciuickly  exhausted.  All  production  which 
has  been  made  has  ])een  by  "dry  placer  methods." 

Of  recent  years,  larfre  scale  attempts  to  work  the  auriferous  gravels 
known  to  occur  in  the  quadrangle  have  been  made.  The  writer  had  the 
privileu'e  of  obscrvina-  several  of  tlic  operations  wliidi  wore  in  |)rogress 
in  1!»28-1924. 

The  economic  gravels  may  for  convenience  be  grouped  into  four 
areas.  The  first  of  these  areas  consists  of  the  gravels  in  the  vicinity 
of  Summit  Digginirs.  The  second,  the  alluvium  in  the  valley  to  the 
nortli  of  but  adjacent  to  the  Rand  Mountains.  The  third  consists  of 
deposits  in  various  gulches  in  the  Stringer  District,  exhausted  of  their 
gold  content  many  years  ago,  but  reworked  during  the  war  for  their 
content  of  placer  scheelite.  And  the  fourth  area,  the  alluvium  s'outh- 
east  of  Atolia,  locally  termed  'the  Atolia  spud  patch,'  which  was  an 
important  source  of  scheelite  during  the  war  period. 

Atolia  'Spud   Patch.' 

During  the  war  high-grade  placer  scheelite  deposits  were  worked 
southeast  of  the  Atolia  ^lill,  over  an  area  a  mile  or  more  in  length  ])y 
V4  to  V2  mile  in  width.  The  source  of  the  scheelite  \vas  undoubtedly 
the  veins  in  the  vicinity  of  Atolia. 

The  s-cheelite  occurred  in  alluvium  of  comparatively  recent  age  at 
dei)ths  of  from  2  to  55  feet.  Locally  this  alluvium  was  cemented  with 
'caliche.'  Deeper  'alluvium'  is  reported  to  have  been  barren  of 
scheelite.  A  shaft  sunk  to  the  southeast  of  the  'spud  patch'  passed 
through  2'50  feet  of  these  deeper  barren  gravels.  This  deep  'alluvium' 
probably  represents  the  Rosamond  formation,  which  is  known  to 
underlie  part  of  this  area. 

The  scheelite  fragments,  termed  'spuds'  by  the  miners,  occurred  in 
various  sizes,  from  fine  sand  up  to  pieces  weighing  several  hundi'cd 
pounds.  The  scheelite  was  not  contined  to  any  s'pecial  horizon  in  the 
alluvium,  but  occurred  concentrated  in  channels  at  various  depths. 
A  number  of  pieces  of  cinnabar  were  found  associated  with  the 
scheelite. 

All  the  scheelite  obtained  from  these  deposits  was  recovered  by  dry 
placer  methods.  No  reliable  figures  representing  the  production  of 
placer  scheelite  could  be  obtained.  It  is  believed,  however,  tli;i1  the 
value  of  the  jir-oduct  would  be  represented  in  seven  figures. 

Huelsdonk   Placer. 

The  Huelsdonk  Dredging  Company,  Inc.,  better  know'n  locally  as  the 
'Norden  Placer,'  holds  9  placer  claims  totaling  over  120  acres  and 
known  as  the  Plat  Gold  Group,  located  in  Sec.  22,  several  miles  noi-th 
of  Randsburg. 

The  property  has  been  sampled  by  means  of  16  shafts  from  15  to  34 
feet  deep.  Eleven  of  these  reached  bedrock.  The  average  values  from 
2'5()  yards  of  material  taken  from  these  shafts  for  sampling  was  80^  per 
yard  for  4  to  16  feet  of  overburden  and  .$2.00  per  yard  for  the  under- 
lying gravels  which  averaged  12  feet  in  thickness.    These  values,  it  w^as 

10—37841 


—  146  — 

stated,  were  obtained  on  a  Stebbins  Dry  Concentrating  machine  with 
an  estimated  recovery  of  80%. 

The  gravels  are  quite  unassorted,  containing  many  large  boulders. 

PLATE  31. 


A.      DREDGE   INSTALLATION    ON    THE   NORDEN   PLACER   CLAIMS. 


B.    STEBBINS    DRY    CONCENTRATOR    ON    THE    PROPERTY    OF    THE    ORO 

FINO  MINING  COMPANY. 

They  are  tightly  packed  and  locally  cemented  with   'caliche.'     The 
bedrock  is  schist. 

The  gold  recovered  possesses  a  value  of  $18.48  per  oz.    The  average 
size  is  such  that  10  colors  yield  a  value  of  Ic.     Pieces  ha^•ing  values 


—  147  — 

as  hiijh  as  20^  were  obtained  in  the  sampling.  The  gold  is  not  con- 
fined to  definite  horizons,  hut  occurs  rather  evenly  distributed  through- 
out tlie  gravels. 

In  the  fall  of  1923  a  suction  dredge  mounted  on  two  pontoons  was 
constructed  in  a  hole  40  by  50  feet  which  had  been  excavated  for  that 
purpose.  The  dredge  was  equipped  with  a  rake  and  crusher  for 
breaking  the  gravels,  a  suction  tul)e  and  pump,  a  grizzley  and  five 
Huelsdonk  concentrating  tables.  These  tables  are  open  boxes  6  inches 
wide  by  18  feet  long  with  grooves  running  lengthwise  on  the  bottom 
of  the  boxes.  A  lengthwise  reciprocating  motion  is  imparted  to  the 
boxes. 

The  cost  of  operation,  it  was  estimated  in  advance,  would  be  Q^  per 
yard,  with  a  daily  capacity  of  500  to  750  yards,  and  an  estimated  daily 
loss  of  water  of  40%.  The  cost  of  water  is  $1.25  per  1000  gallons  at 
the  dredge,  being  obtained  from  the  Yellow  Aster  pipe  line. 

The  writer  did  not  see  the  trial  of  the  dredge,  but  was  informed  that 
water  Avas  run  into  the  excavation  for  five  days  at  the  rate  of  3000 
gallons  per  hour,  the  dredge  being  off  the  bottom  for  perhaps  20 
minutes  during  the  third  day.  The  dredge  was  not  in  operation  in 
Jaiuiary,  1924,  and  no  production  has  been  made. 

Oro   Fino    Placer. 

The  Oro  Fino  Mining  Company  holds  five'  and  a  fraction  claims  near 
Summit  Diggings,  south  of  the  railroad.  Many  old  workings  left  by 
former  small-scale  dry-placering  operations  exist  on  the  property.  The 
property  has  been  worked  intermittently,  it  is  stated,  for  30  years. 

The  gravels,  which  are  widespread  and  not  related  to  recent  streams, 
are  stated  to  average  18  feet  in  thickness.  They  are  unassorted  and 
contain  many  large  boulders.  Locally,  they  show  bedding  and  cross- 
bedding.     They  are  compact  but  only  lightly  cemented. 

It  is  stated  that  the  average  value  of  the  gravels  is  in  excess  of  $2.00 
per  cubic  yard  in  gold.  In  addition,  there  is  a  small  amount  of  flake 
platinum  (determined  by  a  local  assayer  and  not  checked  by  the  writer) 
and  silver,  the  latter  said  to  be  present  as  cerargyrite  to  the  amount  of 
60<*  per  yard.  The  gold  has  a  value'  of  $17.50  to  $19.40  per  oz.  The 
values  are  distributed  throughout  the  gravels,  though  occasionally  local 
concentrations  occur  with  values  up  to  $35.00  or  more  per  cubic  yard. 
The  gold  is  chiefly  coarse,  individual  pieces  having  a  value  of  |^  up. 

A  Stebbins  dry  concentrator  was  installed  during  the  fall  of  1923. 
The  gravel  was  mined  by  a  tractor,  sub-soiler  and  scraper  and  dumped 
on  a  grizzley.  The  undersize  was  then  broken  and  passed  through  a 
trommel.  The  undersize  from  this,  after  having  the  dust  removed  in 
an  air  blast,  was  passed  over  shaking  tables.  The'  tailings  were  stacked 
to  one  side  with  a  stacker.  The  entire  plant  is  portable,  being  mounted 
on  rails.  It  weighs  11  tons.  The  equipment  has  a  capacity  of  150 
yards  of  gravel  per  shift. 

The  plant  was  operated  in  the  fall  of  1923,  approximately  8000  cubic 
yards  of  gravel  being  treated.  It  is  stated  that  the  recovery  was  from 
94%  to  96%,  as  based  on  fire  assays  of  heads,  concentrates  and  tails. 
Much  of  the  gold  recovered  was  coarse,  nuggets  up  to  $4.25  in  value 
being  obtained.  The  total  value  of  the  concentrates  produced  is  not 
known. 


—  148  — 

Approximately  $10,000  was  expended  on  the  plant  and  operations, 
including  a  $1,000  payment  on  the  claims.  The  property  was  not  being 
operated  in  January,  1924. 

Summit  Placer  Gold  and   Rock  Company,  Inc. 

The  Summit  Placer  Gold  and  Rock  Company  holds  12  claims  north 
of  those  held  by  the  Oro  Fino  Mining  Company.  Much  of  the  gravels 
which  it  is  planned  to  work  on  these  claims  consists  of  reconcentrations 
of  the  older  alluvium  in  recent  watercourses.  The  gravels  are  stated  to 
assay  from  $0.80  to  $2.00  per  cubic  vard,  the  average  behiu'  between 
$1.20  and  $1.40. 

It  is  planned  to  install  equipment  in  the  near  future  consisting  of  a 
screening  plant,  dry  concentrating  tables,  and  a  stacking  plant,  having 
a  capacity  of  2000  cubic  yards  per  shift.  The  plant,  which  is  to  be 
mobile,  will  have  a  working  radius  of  75  feet,  the  gravels  being  mined 
by  drag-line  buckets.  The  cost  of  the  plant,  is  is  estimated,  Avill  be 
$65,000. 

It  is  planned  to  market  the  gravels  as  a  by-product  after  their  gold 
content  has  been  removed,  since  the  property  immediately  adjoins  the 
railroad. 

OTHER  ECONOMIC   DEPOSITS. 

Abundant  tuff  deposits  exist  within  the  Randsburg  ouadrangle.  It 
is  possible  that  certain  of  these  may  be  of  such  a  quality  and  so  located 
that  they  can  be  economically  exploited  for  abrasives.  A  small  produc- 
tion has  already  been  made  from  such  a  deposit  located  in  the  Lava 
Mountains  a  few  miles  northeast  of  Summit  Diggings. 

Certain  of  the  beds  of  talc  schist  in  the  Rand  Mountains  have 
economic  possibilities.  Specimens  seen  by  the  writer  were  quite'  pure 
and  of  good  quality.     Some  of  the  beds  are  several  feet  in  thickness. 

Manganese  deposits  are  also  stated  to  occur  in  the  Rand  Mountains, 
presumably  associated  with  quartzites.  These  were  not  visited  by  the 
writer.     Some  production  of  manganese  has  already  been  made. 


INDEX. 


A  Page 

Acaley  mine,  description  of 126 

Accessibility    of    region 13 

Acknowledgments    12 

Age  of  ore  deposits 106 

Alameda   mine , 144 

Aleutites 57 

Alluvium 60 

Amity  mine,  description  of 126 

Andesite  Hows,  description  of 55 

Archean   age,    rocks   of 21-32 

description  of 21,  23 

Atolia  Mining  Co.,  properties  of 125-128 

production    of   127 

Atolia  'spud  patch' 145 

Atilla  mine,  description  of 126 

B 

Baltic  property,  description  of  128 

Basalt,    description    of   53,  60 

Batliolithic  invasion,  after  effects  of 38 

meclianics    of    39 

Beehive  property,  description  of 128 

Belcher  Extension  property,   description  of 128 

Ben  Hur  property,  description  of 129 

Extension,    description   of 129 

Bevis  Divide,  description  of 129 

Bibliography  of  the  Randsburg  quadrangle 15 

Big  Four,  shaft,  description  of 129 

Gold  property,  description  of 130 

Six,   description   of 130 

Black  Hawk  mine,  description  of 130 

Bray  and  Bisbee  workings,  description  of 131 

Bully  Boy  property,  description  of 132 

Butte  mine,  description  of 132 

C 

California  Rand  Silver  mine 110-121 

costs    121 

production   of   . 119 

structure  of    95-96 

veins  of 112-119 

Cerargyrite,   occurrence   of   99,  102 

Chicken  Hawk  mine,  description  of 132 

Cima  Bimetallic  mine,  description  of 132 

Climate    18 

Consolidated  property,  description  of 132 

Contact   metamorphism   37 

Continental  deposits 42 

Coyote  workings,  description  of 133 

Cuve  property,  description   of 134 

D 

Diabase,  description  of 53 

E 

Economic  geology 69-107 

El  Paso  range , 18 

geology  of 31-33 

structure  of    , 31 

Enrichment 86,  102 

Epithermal    deposits    77,  88,  104 

F 

Faulting     62-65 

Field   work   11 

Flat  Iron  mine,  description  of 127 

Tire  property,   description  of 134 


150  INDEX. 

Page 

Fossils,  occurrence  of  33 

Fox  Lease  shaft,  description  of 134 

No.  2  sliaft,  description  of 134 

G 

Garford  Lease  workings,  description  of 135 

Garlock  fault 62 

Geologic    history    65-68 

Geology  of  the  district 20-68 

summary  of    20 

Gimlet  property,  description  of 144 

Gneisses,  description  of i     21 

origin  of    23 

Gold  Bug  mine 144 

Coin  mine 144 

Gold,   fineness  of 88 

deposits,  structure  of 80 

mineralization    79-91 

ores,  grade  of 1 86 

mineralogy  of    83 

origin  of    88 

textures  and  paragenesis 84 

Good  Morning  mine •■ 144 

Grady  Extension  mine 144 

Gravels 61 

H 

Hard  Tack  property,  description  of 135 

Historj'  of  mining 108 

Huelsdonk  placer    145 

Hummer  property,  description  of 135 

Hydrothermal  silicification 50-59 

Hypothermal  veins 38 

I 

Igneous  effusive  rocks 55,  58 

intrusive  rocks ■ 33,  48,  52,  56,  58 

J 

Jersey  Lily  mine 144 

Joberg  Divide  mine    ^ 144 

Johannesburg  gneiss,  description  of 21 

Julius  Shades  property,   description  of 135 

K 

Kelly  Rand  Extension  mine,  description  of 1?6 

King  Solomon  mine,   description  of 136 

L 

La  Crosse  mine 144 

Latite,  described 49 

Lavas,   described   55,  58 

Lava  Mountains    17 

geology  of 42,  55 

structure    of   64 

Literature    13 

Little  Butte  mine,  description  of 1'37 

•lack  mine 144 

Location  of  the  district 1'4 

M 

Mahood  mine,    description  of 126 

Manganese  deposits    148 

Marine   sediments    31 

Metamorphic  rocks  described 21,  23 

Metamorphism,    conditions    of    28,  29 

Miargj-rite,   occurrence  of 101 

Mineral    deposits    69-107 

summary  of 69 

Mineralogy  of  the  ore  deposits 72,  83,  97 

Mines  and  prospects 110-148 

Mining,  history  of 108 

Minnehaha  mine,   description  of 137 

Mizpah  Montana  mine,  description  of 13S 

Nevada  mine,  description  of 138 

Mojave  Rand  mine 144 

Monarch  Rand  property,  description  of 138 


INDEX.  151 

N  PaRo 

Nancy  Hanks  mine,  description  of 139 

Napoleon  mine 144 

Navajo  workings,  description  of 139 

O 

Oney  lease,  description  of 139 

Operator  Divide  mine,  description  of 140 

Orbicular  rocks,  description  of 35 

Ore  deposition,  structural  control  of 76,  88,  105 

deposits,    structure    of    70,  80,  9,5 

Ores,   grade  of 74,86,99 

mineralogy   of    72,  83,  97 

origin   o( 77,  88,  104 

Oro  P^ino  placer 147 

Osdick   mine    144 

P 

Paleozoic  age,  rocks  of 31-50 

description   of  rocks  of 31 

Papoose  mine,  description  of 126 

Par  mine,  description  of 127 

Phoenix  mine,  description  of 140 

Pinmore  mine 144 

Placer   deposits    144-148 

Plutonic   rocks   33 

Previous  work  in  the  area 14 

Proustite,   occurrence  of 102 

Pyrargyrite,  occurrence  of 101 

Q 

Quartz  monzonite,  description  of 34 

area  underlain  by 40 

relation  of,  to  adjacent  rocks 37 

R 

Rainstorm  mine,  description  of 127 

Rand  Contact  property,  description  of 140 

Mountain  property,   description   of 140 

■    mountains   17 

geology  of 23 

structure  of    64 

schist,   description   of 23 

Randsburg  Associated  Mines  Co.,  property  of 140 

Ratcliffe   mine    144 

Red  mountain    17 

geolog>'  of 42,  55 

Rosamond  series 42-48 

conditions  of  accumulation 47 

Rhyolites,  description  of 49 

S 
Santa  Fe  shaft 134 

Scheelite,  occurrence  of 74 

Schists,  description  of 23 

origin   of • 26 

Sediments,  continental 42 

marine 31 

Shallow    igneous    intrusives 48,  52,  56,  58 

Silver  Basin  property,  description  of 141 

Bell  property,  description  of 141 

deposits,   structure   of 95 

Giant  shaft,   description   of 141 

Glance  lease 142 

Horde   lease   133 

King  mine,  description  of    142 

mineralization    92—106 

ores,  grade  of 99 

mineralog>'   of   97 

origin  of 104 

texture  and  paragcnesis 99 

Silvertun  shaft,  description  of 143 

Solutions,   nature  of   ore  depositing 77,  88,  105 

South  Rand  property,  description  of 143 

Static  metamorphism 29 

St.   Elmo   mine 144 


152  INDEX. 

Paee 

St.  Lawrence  Rand  property 143 

Structural  control  of  ore  deposition 76,  88,  105 

Structure,   geologic   61 

(See  also  under  individual  formations) 

Stylotypite,  occurrence  of 101 

Summit  range 18 

Summit  Placer  Gold  and  Rock  Co. 148 

Sunshine  mine 144 

Swastika   shaft    139 

T 

Talc   deposits 148 

Tertiary  formations 42-60 

Thirteen    lease    1 133 

Thrust   faults   64 

Towns  of  the  quadrangle 13 

Transportation  into  region 13 

Treasure  hill  property 143 

Tuff    deposits   148 

Tungsten  deposits,  structure  of 70 

mineralization 70-78 

ores,  grade  of 74 

mineralogy   of 72 

origin  of 77 

texture  and  paragenesis 74 

U 

Union  mine,  description  of 125 

V 

Valleys,  character  of 18 

^'egetation     19 

W 
Wall   rocks,    alteration   of 86,  102 

Water  supply 19 

White  Horse  Rand  Shaft 144 

Winnie  mine 144 

Y 

Yellow  Aster  mine,   description  of 121-125 

production 125 

structure   88-90 


,  BUREAU    PUBLICATIONS.  I 

PUBLICATIONS  OF  THE  CALIFORNIA  STATE 
MINING  BUREAU. 

During  the  past  forty-four  years,  in  carrying  out  the  provisions  of 
the  organic  act  creating  the  California  State  Mining  Bureau,  there 
have  been  published  many  reports,  bulletins  and  maps  which  go  to  make 
up  a  library  of  detailed  information  on  the  mineral  industry  of  the 
state,  a  large  part  of  which  could  not  be  duplicated  from  any  other 
source. 

One  feature  that  has  added  to  the  popularity  of  the  publications  is 
that  many  of  them  have  been  distributed  without  cost  to  the  public,  and 
even  the  more  elaborate  ones  have  been  sold  at  a  price  which  barely 
covers  the  cost  of  printing. 

Owing  to  the  fact  that  funds  for  the  advancing  of  the  work  of  this 
department  have  often  been  limited,  many  of  the  reports  and  bulletins 
mentioned  Avere  printed  in  limited  editions  which  are  now  entirely 
exhausted. 

Copies  of  such  publications  are  available,  however,  in  the  Bureau's 
offices  in  the  Ferry  Building,  San  Francisco ;  Pacific  Finance  Building, 
Los  Angeles;  in  Sacramento;  Santa  Maria;  Santa  Paula;  Coalinga; 
Taft;  Bakersfield.  They  may  also  be  found  in  many  public,  private 
and  technical  libraries  in  California  and  other  states,  and  foreign 
countries. 

A  catalog  of  all  publications  of  the  Bureau,  from  1880  to  1917, 
giving  a  synopsis  of  their  contents,  is  issued  as  Bulletin  No.  77. 

Publications  in  stock  may  be  obtained  by  addressing  any  of  the  offices 
of  the  State  Mining  Bureau  and  enclosing  the  requisite  amount  in  the 
case  of  publications  that  have  a  list  price.  The  Bureau  is  authorized 
to  receive  only  coin,  stamps  or  money  orders,  and  it  will  be  appreciated 
if  remittance  is  made  in  this  manner  rather  than  by  personal  check. 

The  prices  noted  include  delivery  charges  to  all  parts  of  the  United 
States.  Money  orders  should  be  made  payable  to  the  State  ]\Iining 
Bureau, 

REPORTS. 

Asterisks  (*•)  indicate  the  publication  is  out  of  print. 

Price 

**First  Annual   Report  of  the  State  Mineralogist,   ISSO,  43  pp.     Henry   G. 

Hanks 

**Second  Annual  Report  of  the  State  Mineralogist,  1882,  514  pp.,  4  illustra- 
tions, 1  map.     Henry  G.  Hanks 

•♦Third  Annual  Report  of  the  State  Mineralogist,  1883,  111  pp.,  21  illustra- 
tions.    Henry   G.   Hanks 

♦♦Fourth  Annual  Report  of  the  State  Mineralogist,  1884,  410  pp.,  7  illustra- 
tions.    Henry   G.   Hanks 

♦♦Fifth  Annual  Report  of  the  State  Mineralogist,  1885,  234  pp.,  15  illustra- 
tions, 1  geological  map.     Henry  G.  Hanks 

♦♦Sixth  Annual  Report  of  the   State  Mineralogist,  Part  I,  1886,  145  pp.,  3 

illustrations.  1  map.     Henry  G.  Hanks 

♦♦Part  II,  1887,  222  pp.,  36  illustrations.     Williana  Irelan,  Jr 

♦♦Seventh  Annual  Report  of  the  State  Mineralogist,  1887,  315  pp.     William 

Irelan,  Jr.  

♦♦Eighth  Annual  Report  of  the  State  Mineralogist,  1888,  MS  pp.,  122  illustra- 
tions.    William   Irelan,  Jr 

♦♦Ninth  Annual  Report  of  the  State  Mineralogist,  1889,  352  pp.,  57  illustra- 
tions, 2  maps.     William  Irelan,   Jr -. 


II  REPORT   OF    STATE    MINERALOGIST. 

REPORTS — Continued. 

Asterisks  (•♦)  Indicate  the  publication  Is  out  of  print. 

Price 
**Tenth  Annual  Report  of  the  State  Mineralogist,  1890,  983  pp.,  179  illustra- 
tions, 10  maps.     William  Irelan,  Jr 

Eleventh  Report   (First  Biennial)    of  the   State  Mineralogist,  for  the  two 
j-ears   ending   September  15,   1892,   612   pp.,   73   illustrations,  4  maps. 

William  Irelan,  Jr $1.00 

♦♦Twelfth  Report   (Second  Biennial)   of  the  State  Mineralogist,  for  the  two 
years  ending  September  15,  1894,  541  pp.,  101   illustrations,  5  maps. 

J.  J.  Crawford 

♦♦Thirteenth  Report  (Third  Biennial)  of  the  State  Mineralogist,  for  the  two 
years   ending   September   15,   1896,   726   pp.,   93   illustrations,   1   map. 

J.  J.  Crawford 

Chapters   of   the    State   Mineralogist's    Report,    Biennial    Period,    1913-1914, 

Fletcher  Hamilton  : 
♦♦Mines  and  Mineral  Resources,  Amador,  Calaveras  and  Tuolumne  Counties, 

172  pp.,   paper ^ 

Mines  and  Mineral  Resources,  Colusa,  Glenn,  Lake,  Marin,  Napa,  Solano, 

Sonoma  and  Yolo  Counties,  208  pp.,  paper .50 

Mines    and    Mineral    Resources,    Del    Norte,    Humboldt,    and    Mendocino 

Counties,  59  pp.,  paper .25 

♦♦Mines   and   Mineral    Resources,   Fresno,   Kern,   Kings,    Madera,    Mariposa, 

Merced,  San  Joaquin  and  Stanislaus  Counties,  220  pages,  paper 

Mines    and    Mineral    Resources    of    Imperial    and    San    Diego    Counties, 

113   pp.,   paper .35 

♦♦Mines    and    Mineral    Resources,    Shasta,    Siskiyou    and    Trinity    Counties, 

180  pp.,  paper 

Fourteenth  Report  of  the  State  Mineralogist,  for  the  Biennial  Period  1913- 
1914,  Fletcher  Hamilton,  1915: 
A  General  Report  on  the  Mines  and  Mineral  Resources  of  Amador,  Cala- 
veras, Tuolumne,  Colusa,  Glenn,  Lake,  Marin,  Napa,  Solano,  Sonoma, 
Yolo,  Del  Norte,  Humboldt,  Mendocino,  Fresno,  Kern.  Kings,  Madera, 
Mariposa,  Merced,  San  Joaquin,  Stanislaus,  San  Diego,  Imperial, 
Shasta,    Siskiyou,    and    Trinity    Counties,    974   pp.,    275    illustrations, 

cloth    2.00 

Chapters   of   the    State   Mineralogist's    Report,   Biennial    Period,    1915-1916, 
Fletcher  Hamilton  : 
Mines  and  Mineral  Resources,  Alpine,  Inyo  and  Mono  Counties,  176  pp., 

paper    .65 

Same,  including  geological  map  of  Inyo  County 1.25 

Mines  and  Mineral  Resources,  Butte,  Lassen.  Modoc,   Sutter,  and  Tehama 

Counties,   91  pp.,   paper .50 

Mines  and  Mineral  Resources,   El   Dorado,  Placer,   Sacramento,  and  Yuba 

Counties,  198  pp.,   paper .65 

Mines   and   Mineral   Resources,   Monterey,   San   Benito,    San   Luis   Obispo, 

Santa  Barbara,  and  Ventura  Counties,  183  pp.,  paper .65 

Mines  and  Mineral  Resources,  Los  Angeles,  Orange,  and  Riverside  Counties, 

136   pp.,    paper .50 

Mines  and  Mineral  Resources,  San  Bernardino  and  Tulare  Counties,  186  pp., 

paper .65 

Fifteenth  Report  of  the  State  Mineralogist,  for  the  Biennial  Period  1915- 
1916,  Fletcher  Hamilton,  1917: 
A  General  Report  on  the  Mines  and  Mineral  Resources  of  Alpine,  Inyo, 
Mono,  Butte,  Lassen,  Modoc,  Sutter,  Tehama,  Placer,  Sacramento, 
Yuba,  Los  Angeles,  Orange,  Riverside,  San  Benito,  San  Luis  Obispo, 
Santa  Barbara,  Ventura,  San  Bernardino  and  Tulare  Counties,  990  pp., 

413  illustrations,  cloth 3.75 

Chapters    of    the    State    Mineralogist's    Report,    Biennial    Period    1917-1918, 
Fletcher  Hamilton  : 

Mines  and  Mineral  Resources  of  Nevada  County,  270  pp.,  paper .75 

Mines  and  Mineral  Resources  of  Plumas  County,  188  pp.,  paper .50 

Mines  and  Mineral  Resources  of  Sierra  County,  144  pp.,  paper .50 

Seventeenth   Report  of   the   State   Mineralogist,   1920,    Mining   in   California 

during  1920,  Fletcher  Hamilton ;  562  pp.,  71  illustrations,  cloth 1.75 


BUREAU    PUBLICATIONS.  Ill 

REPORTS — Continued. 

Asterisks  (**)  indicate  the  publication  is  out  of  print. 

Price 
Eighteenth    Report   of   the   State   Mineralogist,    1922,   Mining   in   California, 
Fletcher  Hamilton.     Chapters  published  monthly  beginning  with  Jan- 
uary, 1922: 
♦♦January,  ♦♦February,  March,  April,  May,  June,  July,  August,  September, 

October,  November,  December,  1922 Free 

Chapters  of  Nineteenth  Report  of  the  State  Mineralogist,  'Mining  in  California,' 
Fletcher  Hamilton  and  Lloyd   L.  Root.     January,   February,   March, 

September,  1923 Free 

Chapters  of  Twentieth  Report  of  the  State  Mineralogist,  'Mining  in  California,' 
Lloyd  L.  Root.     Published  quarterly.     January,  April,  July,  October, 

1924,  per  copy $0.25 

Chapters  of  Twenty-first  Report  of  State  Mineralogist.  Mining  in  California, 

Lloj'd  L.  Root.     Published  quarterly.     January,  1925 .25 

Subscription,  $1.00  in  advance   (by  calendar  year,  only). 
Chapters  of  State  Oil  and  Gas  Supervisor's  Report : 

Summary  of  Operations — California  Oil  Fields,  July,  1918,  to  March,  1919 

(one  volume)    Free 

Summary   of  Operations — California   Oil   Fields.      Published    monthly,   begin- 
ning April,  1919 : 
♦♦April,  ♦♦May,  June,  ♦♦July,  ♦♦August,  ♦♦September,  ♦♦October,  November, 

♦♦December,  1919 Free 

January,  February,  March,  April,  ♦♦May,  June,  July,  ♦♦August,  September, 

October,   November,  December,  1920 Free 

January,    ♦♦February,    ♦♦March,    ♦♦April,    May,    June,    ♦♦July,    August, 

♦♦September,  ♦♦October,  ♦♦November,  ♦♦December,  1921 Free 

January,    February,    March,   April,   May.   June,   July,    August,    September, 

October,  November,   December,  1922 Free 

January,   February,   March,   April,   May,   June,   July,   August,    September, 

October,  November,  December,  1923 Free 

January,  February.  March,  April,  May,  June,  July,  August,  September,  1924     Free 

BULLETINS. 

Asterisks    (*•)    Indicate    the   publication    Is   out  of   print. 

♦♦Bulletin  No.  1.     A   Description   of   Some   Desiccated  Human   Remiains,   by 

Winslow  Anderson.     1888,  41  pp.,  6  illustrations 

♦♦Bulletin  No.  2.     Methods   of  Mine  Timbering,    by   W.   H.    Storms.     1894, 

58  pp.,  75  illustrations 

♦♦Bulletin  No.  3.     Gas  and  Petroleum  Yielding  Formations  of  Central  Valley 

of  California,  by  W.  L.  Watts.    1894,  100  pp.,  13  illustrations,  4  maps.     

♦♦Bulletin  No.  4.     Catalogue  of  Californian   Fossils,  by  J.  G.  Cooper,  1894, 

73  pp.,  67  illustrations.     (Part  I  was  published  in  the  Seventh  Annual 

Report  of  the  State  Mineralogist,  1887.) 

♦♦Bulletin  No.  5.     The  Cyanide  Process,  1894,  by  Dr.  A.  Scheidel.     140  pp., 

46  illustrations 

Bulletin  No.  6.     California   Gold  Mill   Practices,   1895,   by   E.  B.   Preston, 

85  pp.,  46  illustrations .50 

♦♦Bulletin  No.  7.     Mineral    Production    of    California,    by    Counties    for    the 

year  1894,  by  Charles  G.  Yale.     Tabulated  sheet 

♦♦Bulletin  No.  8.     Mineral    Production    of   California,    by    Counties    for   the 

year  1895,  by  Charies  G.  Yale.     Tabulated  sheet 

♦♦Bulletin    No.   9.     Mine   Drainage,   Pumps,   etc.,   by   Hans  C.   Behr.     1896, 

210  pp.,  206  illustrations 

**Kulletin  No.  10.     A  bibliography  Relating  to  the  Geology,  Palaeontology  and 

Mineral  Resources  of  California,  by  Anthony  W.  Vogdes.    1896,  121  pp.     

♦♦Bulletin  No.  11.     Oil  and  Gas  Yielding  Formations  of  Los  Angeles,  Ventura 

and  Santa  Barbara  counties,  by  W.  L.  Watts.     1897,  94  pp.,  6  maps, 

31  illustrations 

♦♦Bulletin  No.  12.     Mineral  Production  of  California,  by  Counties  for  1896, 

by  Charles  G.  Yale.     Tabulated  sheet 

♦♦Bulletin  No.  13.     Mineral  Production  of  California,  by  Counties  for  1897, 

by  Charles  G.  Yale.     Tabulated  sheet 


IV  REPORT   OF   STATE    MINERALOGIST. 

BULLETINS— Continued. 

Asterisks  (•♦)  Indicate  the  publication  Is  out  of  print. 

Price 
♦♦Bulletin  No.  14.     Mineral  Production  of  California,  by  Counties  for  1898, 

by  Charles  G.  Yale 

♦♦Bulletin   No.   15.      Map   of   Oil   City   Fields,   Fresno  County,   by   John   H. 

Means.     1899   

♦♦Bulletin  No.  16.     The  Genesis  of  Petroleum  and  Asphaltum  in  California, 

by  A.  S.  Cooper.     1899,  39  pp.,  29  illustrations 

♦♦Bulletin  No.  17.     Mineral  Production  of  California,  by  Counties  for  1899, 

by  Charles  G.  Yale.    Tabulated  sheet 

♦♦Bulletin   No.   IS.     Mother  Lode  Region   of  California,  by   W.   H.   Storms. 

1900,  154  pp.,  49  illustrations 

♦♦Bulletin  No.  19.     Oil  and  Gas  Yielding  Formations  of  California,  by  W.  L. 

Watts.     1900,  236  pp.,  60  illustrations,  8  maps 

♦♦Bulletin  No.  20.     Synopsis  of  General  Report  of  State  Mining  Bureau,  by 

W.  L.  Watts.     1901,  21  pp.     This  bulletin  contains  a  brief  statement 

of  the  progress  of  the  mineral  industry  in  California  for  the  four  years 

ending  December,  1899 

♦♦Bulletin  No.  21.     Mineral  Production  of  California  by  Counties,  by  Charles 

G.  Yale.     1900.     Tabulated  sheet 

♦♦Bulletin  No.  22.     Mineral  Production  of  California  for  Fourteen  Years,  by 

Charles  G.  Yale.     1900.    Tabulated  sheet 

Bulletin  No.  23.     The  Copper  Resources  of  California,  by  P.  C.  DuBois, 

F.  M.  Anderson,  J.  H.  Tibbits  and  G.  A.  Tweedy.     1902,  282  pp.,  69 
illustrations,  and  9  maps $0.50 

♦♦Bulletin  No.  24.    The  Saline  Deposits  of  California,  by  G.  E.  Bailey.    1902, 

216  pp.,  99  illustrations,  5  maps 

♦♦Bulletin  No.  25.     Mineral  Production  of  California,  by  Counties,  for  1901, 

by  Charles  G.  Yale.    Tabulated  sheet 

♦♦Bulletin   No.  26.     Mineral   Production  of  California   for  the  past  Fifteen 

Years,  by  Charles  G.  Yale.     1902.    Tabulated  sheet 

♦♦Bulletin    No.    27.     The   Quicksilver   Resources   of   California,    by   William 

Forstner.     1903,  273  pp.,  144  illustrations,  8  maps 

♦♦Bulletin  No.  28.     Mineral  Production  of  California,   for  1902,  by  Charles 

G.  Yale.     Tabulated  sheet 

♦♦Bulletin  No.  29.     Mineral  Production  of  California  for  Sixteen  Years,  by 

Charles  G.  Yale.     1903.     Tabulated  sheet 

**Bu]letin  No.  30.     Bibliography  Relating  to  the  Geology,  PaliEontology,  and 

Mineral  Resources  of  California,  by  A.  W.  Vogdes.    1903,  290  pp 

♦♦Bulletin   No.  31.     Chemical   Analyses   of  California  Petroleum,  by  H.   N. 

Cooper.     1904.     Tabulated  sheet 

♦♦Bulletin  No.  32.     Production  and  Use  of  Petroleum  in  California,  by  Paul 

W.  Prutzman.     1904,  230  pp.,  116  illustrations,  14  maps 

♦♦Bulletin  No.  33.     Mineral  Production  of  California,  by  Counties,  for  1903, 

by   Charles   G.   Yale.     Tabulated   sheet 

♦♦Bulletin   No.  34.     Mineral   Production  of  California   for  Seventeen  Years, 

by  Charles  G.  Yale.     1904.     Tabulated  sheet 

♦♦Bulletin   No.  35.     Mines  and  Minerals  of  California,  by  Charles  G.  Yale. 

1904,  55  pp.,  20  county  maps.     Relief  map  of  California 

**Bulletin  No.  36.     Gold  Dredging  in  California,  by  J.  E.  Doolittle.     1905, 

120  pp.,  66  illustrations,  3  maps 

^-^Bulletin  No.  37.     Gems,    Jewelers'    Materials,    and    Ornamental    Stones   of 

California,  by  George  F.  Kunz.     1905,  168  pp..  .54  illustrations .25 

♦♦Bulletin   No.  38.      Structural   and   Industrial    Materials   of  California,   by 

Wm.  Forstner,  T.  C.  Hopkins,  C.  Naramore  and  L.  H.  Eddy.     1906, 

412  pp.,  150  illustrations,  1  map 

♦♦Bulletin  No.  39.     Mineral  Production  of  California,  by  Counties,  for  1904, 

by  Charles  G.  Yale.     Tabulated  sheet 

♦♦Bulletin   No.   40.      Mineral   Production   of  California   for   Eighteen  Years, 

by  Charles  G.  Yale.     1905.     Tabulated  sheet 

♦♦Bulletin  No.  41.     Mines  and  Minerals  of  California,  for  1904,  by  Charles 

G.  Yale.     1905,  54  pp.,  20  county  maps 

♦♦Bulletin  No.  42.     Mineral  Production  of  California,  by  Counties,  1905,  by 

Charles  G,  Yale.     Tabulated  sheet 


BUREAU    PUBLICATIONS.  V 

BULLETINS— Continued. 

Asterisks  (••)  Indicate  the  publication  Is  out  of  print. 

Price 
♦♦Bulletin   No.   43.      Mineral   Production   of   California   for   Nineteen   Years, 

by  Charles  G.  Yale.     Tabulated  sheet 

♦♦Bulletin   No.  44.     California  Mines  and  Minerals  for  1905,  by  Charles  G. 

Yale.     1907,  31  pp.,  20  county  maps 

♦♦Bulletin  No.  45.     Auriferous  Black  Sands  of  California,  by  J.  A.  Edman. 

1907.     10  pp 

Bulletin   No.  46.     General   Index  of  Publications  of  the   California   State 

INIining  Bureau,  by  Charles  G.  Yale.     1907,  54  pp $0.30 

♦♦Bulletin    No.   47.      Mineral   Production   of   California,    by   Counties,   1906, 

by  Charles  G.  Yale.     Tabulated  sheet 

♦♦Bulletin    No.   48.      Mineral    Production    of   California    for   Twenty    Years. 

1906,  by  Charles  G.  Yale 

♦♦Bulletin  No.  49.     Mines  and  Minerals  of  California  for  1906,  by  Charles 

G.   Yale.     34   pp 

Bulletin  No.  50.     The  Copper  Resources  of  California,  1908,  by  A.  Haus- 

mann,  J.  Kruttschuitt,  Jr.,  W.  E.  Thome  and  J.  A.  Edman,  366  pp., 

74  illustrations.      (Revised  edition.) 1.00 

♦♦Bulletin  No.  51.     Mineral  Production  of  California,  by  Counties,  1907,  by 

D.  H.  Walker.     Tabulated  sheet 

♦♦Bulletin  No.  52.     Mineral  Production  of  California  for  Twenty-one  Years, 

1907,  by  D.  H.  Walker.     Tabulated  sheet 

♦♦Bulletin  No.  53.     Mineral  Production  of  California  for  1907,  with  County 

Maps,  by  D.  H.  Walker,  62  pp 

♦♦Bulletin  No.  54.     Mineral  Production  of  California,  by  Counties,  by  D.  H. 

Walker,  1908.     Tabulated  sheet 

♦♦Bulletin  No.  55.     Mineral  Production  of  California  for  Twenty-two  Years, 

by  D.  H.  Walker,  1908.     Tabulated  sheet 

♦♦Bulletin   No.   56.     Mineral   Production   for   1908,   with   County   Maps   and 

Mining  Laws  of  California,  by  D.  H.  Walker.     78  pp 

♦♦Bulletin   No.   57.     Gold   Dredging   in   California,   by   W.   B.   Winston   and 

Chas.  Janin.    1910,  312  pp.,  239  illustrations  and  10  maps 

"*Bullotiu   No.  58.     Mineral  Production  of  California,  by  Counties,  by  D.  H. 

Walker,  1909.     Tabulated  sheet 

♦♦Bulletin  No.  59.     Mineral  Production  of  California  for  Twenty-three  Years, 

by  D.  H.  Walker,  1909.     Tabulated  sheet 

♦♦Bulletin  No.  60.     Mineral  Production  for  1909,  County  Maps  and  Mining 

Laws  of  California,  by  D.  H.  Walker.     94  pp 

♦♦Bulletin  No.  61.     Mineral  Production  of  California,  by  Counties  for  1910, 

by  D.  H.  Walker.    Tabulated  sheet 

♦♦Bulletin  No.  62.     Mineral  Production  of  California  for  Twenty-four  Years, 

by  D.  H.  Walker,  1910.     Tabulated  sheet 

♦♦Bulletin  No.  63.     Petroleum  in  Southern  California,  by  P.  W.  Prutzman. 

1912,  430  pp.,  41  illustrations,  6  maps 

♦♦Bulletin  No.  64.     Mineral  Production  for  1911,  by  E.  S.  Boalich.     49  pp.__     

♦♦Bulletin  No.  65,     Mineral  Production  for  1912.  by  E.  S.  Boalich.      64  pp.—     

♦♦Bulletin  No.  66.     Mining  Laws  of  the  United  States  and  California.     1914, 

89  pp.  — - 

♦♦Bulletin    No.    67.      Minerals    of   California,    by    Arthur    S.    Eakle.      1914, 

226    pp.    

♦♦Bulletin   No.   68.      Mineral   Production   for  1913,   with   County   Maps   and 

Mining  Laws,  by  E.  S.  Boalich.     160  pp 

♦♦Bulletin   No.  69,     Petroleum   Industry  of  California,   with   Folio  of  Maps 
(18  by  22),  by  R.  P.  McLaughlin  and  C.  A.  Waring.     1914,  519  pp., 

13  illustrations,  83  figs.     [18  plates  in  accompanying  folio.] 

♦♦Bulletin   No.   70.     Mineral   Production    for   1914,   with  County   Maps   and 

Mining  Laws.     184   pp 

♦♦Bulletin    No.   71.     Mineral   Production   for   1915,   with   County   Maps   and 

Mining  Laws,  by  Walter  W.  Bradley.     193  pp.,  4  illustrations 

Bulletin  No.  72.     The  Geologic  Formations  of  California,  by  James  Perrin 

Smith.     1916,  47   pp .25 

Reconnaissance  Geologic  Map   (of  which.  Bulletin  72  is  explanatory), 

in  23  colors.     Scale :  1  inch  equals  12  miles.     Mounted 2.50 


VI  REPORT    OF    STATE    MINERALOGIST. 

BULLETINS— Continued. 

Asterisks  (♦•)  Indicate  the  publication  Is  out  of  print. 

Price 
♦♦Bulletin   No.  73.     First  Annual  Report  of  the  State  Oil  and  Gas  Super- 
visor of  California,  for  the  fiscal  year  1915-16,  by  R.  P.  McLaughlin. 
278  pp.,  26  illustrations 

Bulletin  No.  74.     Mineral  Production  of  California  in  1&16,  with  County 

Maps,  by  Walter  W.  Bradley.     179  pp.,  12  illustrations Free 

♦♦Bulletin  No.  75.     United  States  and  California  Mining  Laws,  1917.    115  pp., 

paper 

Bulletin  No.  76.  Manganese  and  Chromium  in  California,  by  Walter  W. 
Bradley,  Emile  Huguenin,  C.  A.  Logan,  W.  B.  Tucker  and  C.  A. 
Waring,  1918.     248  pp.,  51  illustrations,  5  maps,  paper $0.50 

Bulletin    No.   77.     Catalogue   of   Publications   of   California   State   Mining 

Bureau,  1880-1917,  by  E.  S.  Boalich.     44  pp.,  paper Free 

Bulletin  No.  78.  Quicksilver  Resources  of  California,  with  a  Section  on 
Metallurgy  and  Ore-Dressing,  by  Walter  W.  Bradley,  1918.  389  pp., 
77  photographs  and  42  plates  (colored  and  line  cuts),  cloth 1.50 

Bulletin  No.  79.     Magnesite  in  California.      (In  preparation.) 

Bulletin    No.    80.     Tungsten,    Molybdenum    and    Vanadium    in    California. 

(In    preparation.)    

Bulletin  No.  81.     Foothill  Copper  Belt  of  California.     (In  preparation.)—     

♦♦Bulletin  No.  82.  Second  Annual  Report  of  the  State  Oil  and  Gas  Super- 
visor, for  the  fiscal  year  1916-1917,  by  R.  P.  McLaughlin,  1918.  412  pp., 
31   illustrations,   cloth 

Bulletin    No.   83.     California   Mineral   Production    for   1917,   with  Cotinty 

Maps,  by  Walter  W.  Bradley.     179  pp.,  paper Free 

♦♦Bulletin  No.  84.  Third  Annual  Report  of  the  State  Oil  and  Gas  Saper- 
visor,    for    the    fiscal    year    1917-1918,    by    R.    P.    McLaughlin,    1918. 

617  pp.,  28  illustrations,  cloth 

♦♦Bulletin  No.  85.    Platinum  and  Allied  Metals  in  California,  by  C.  A.  Logan, 

1919.     10  photographs,  4  plates,  120  pp.,  paper .50 

Bulletin    No.   86.     California   Mineral   Production   for  1918,   with   County 

Maps,  by  Walter  W.  Bradley,  1919.     212  pp.,  paper Free 

♦♦Bulletin  No.  87.  Commercial  Minerals  of  California,  with  notes  on  their 
uses,  distribution,  properties,  ores,  field  tests,  and  preparation  for 
market,  by  W.  O.  Castello,  1920.     124  pp.,  paper 

Bulletin    No.   88.     California   Mineral   Production    for  1919,   with   County 

Maps,  by  Walter  W.  Bradley,  1920.     204  pp.,  paper Free 

**Bulletin  No.  SO.  Petroleum  Resources  of  California,  with  Special  Reference 
to  Unproved  Areas,  by  Lawrence  Vander  Leek,  1921.  12  figures,  6 
photographs,  6  maps  in  pocket,  186  pp.,  cloth 1.25 

Bulletin   No.   90.     California   Mineral    Production   for   1920,    with   County 

Maps,  by  Walter  W.  Bradley,  1921.     218  pp.,  paper Free 

Bulletin  No.  91.     Minerals  of  California,  by  Arthur  S.  Eakle,  1923,  328  pp., 

cloth    1.00 

Bulletin  No.  92.  Gold  Placers  of  California,  by  Chas.  S.  Haley,  1923.  167 
pp.,  36  photographs  and  7  plates   (colored  and  line  cuts,  also  geologic 

map),    cloth    1.50 

E.xtra  copies  of  the  Geologic  Map  (in  4  colors) .50 

Bulletin  No.  93.     California  Mineral  Production  for  1922,  by   Walter  W. 

Bradley,  1923 Free 

Bulletin   No.  94.     California  Mineral  Production  for  1923,  by  Walter  W. 

Bradley,  1924 Free 

PRELIMINARY   REPORTS. 
Asterisks  (**)  indicate  the  publication  is  out  of  print. 

♦♦Preliminary  Report  No.  1.     Notes  on  Damage  by  Water  in  California  Oil 

Fields,  December,  1913.     By  R.  P.  McLaughlin.     4  pp 

♦♦Preliminary  Report  No.  2.     Notes  on  Damage  by  Water  in  California  Oil 

Fields,  March,  1914.     By  R.  P.  McLaughlin.     4  pp 

Preliminary   Report  No.  3.     Manganese  and   Chromium,  1917.     By   E.   S. 

Boalich.    32  pp 


BUREAU    PUBLICATIONS.  VII 

PRELIMINARY    REPORTS— Continued. 

Asterisks  (♦♦)  indicate  the  publication  is  out  of  print. 

Price 

Pr'^liminary   Report   No.   4.     Tungsten,    Molybdenum   and   Vanadium.     By 

E.  S.  Boalich  and  W.  O.  Castello,  1918.     34  pp.     Paper Free 

Preliminary  Report  No.  5.     Antimony,  Graphite,  Nickel,  Potash,  Strontium 

and  Tin.  By  E.  S.  Boalich  and  W.  O.  Castello,  1918.  44  pp.  Paper__  Free 
Preliminary  Report  No.  6.     A  Review  of  Mining  in  California  During  1919. 

Fletcher  Hamilton,  1920.     43  pp.  Paper Free 

♦♦Preliminary   Report  No.  7.     The  Clay   Industry   in  California.     By  E.   S. 

Boalich,  W.  O.  Castello,  E.  Huguenin,  C.  A.  Logan,  and  W.  B.  Tucker, 

1920.  102  pp.     24  illustrations.     Paper 

Preliminary    Report   No.   S.     A    Review    of    Mining   in    California   During 

1921,  with   Notes  on  the  Outlook  for  1922.     Fletcher  Hamilton,  1922. 

68  pp.     Paper 

MISCELLANEOUS    PUBLICATIONS. 
Asterisks  (**)   indicate  the  publication  is  out  of  print. 

♦♦First  Annual  Catalogue  of  the  State  Museum  of  California,  being  the  collec- 
tion made  by  the  State  Mining  Bureau  during  the  year  ending  April  16, 
ISSl.     350  pp 

♦♦Catalogue  of  books,  maps,  lithographs,  photographs,  etc.,  in  the  library  of 

the  State  Mining  Bureau  at  San  Francisco,  May  15,  1884.    19  pp 

♦♦Catalogue  of  the  State  Museum  of  California,  Volume  II,  being  the  collec- 
tion made  by  the  State  Mining  Bureau  from  April  16,  1881,  to  May  5, 
1884.     220  pp 

♦♦Catalogue  of  the  State  Museum  of  California,  Volume  III,  being  the  collec- 
tion made  by  the  State  Mining  Bureau  from  May  15,  1884,  to  March  31, 
1887.      195   pp 

♦♦Catalogue  of  the  State  Museum  of  California,  Volume  IV,  being  the  collec- 
tion made  by  the  State  Mining  Bureau  from  March  30,  1887,  to  August 
20,    1890.      261   pp 

♦♦Catalogue  of  the  Library  of  the  California  State  Mining  Bureau,  September 

1,  1892.     149  pp 

♦♦Catalogue  of  West  North  American  and  Many  Foreign  Shells  with  Their 
Geographical  Ranges,  by  J.  G.  Cooper.  Printed  for  the  State  Mining 
Bureau,  April,  1894 

♦♦Report  of  the  Board  of  Trustees  for  the  four  years  ending  September,  1900. 

1.5   pp.      Paper 

Bulletin.      Reconnaissance   of    the   Colorado   Desert    Mining   District.      By 

Stephen  Bowers,  1901.     19  pp.     2  illustrations.     Paper Free 

Commercial    Mineral    Notes.      A    monthly    mimeographed    sheet,    beginning 

April,  1923 Free 

MAPS. 

Registers  of  Mines  With   Maps. 

Asterisks  (*•)  Indicate  out  of  print. 

♦♦R<?gister  of  Mines,  with  Map,  Amador  County 

♦♦Register  of  Mines,  with  Map,  Butte  County 

♦♦Register  of  Mines,  with  Map,  Calaveras  County 

♦♦Register  of  Mines,  with  Map,  El    Dorado    County 

♦♦Register  of  Mines,  with  Map,  Inyo  County  

♦♦Register  of  Mines,  with  Map,  Kern    County    

♦♦Register  of  Mines,  with  Map,  Lake  County 

♦♦Register  of  Mines,  with  Map,  Mariposa  County 

♦♦Register  of  Mines,  with  Map,  Nevada  County 

♦♦Register  of  Mines,  with  Map,  Placer    County    

♦♦Register  of  Mines,  with  Map,  Plumas    County    

♦♦Register  of  Mines,  with  Map,  San  Bernardino  County 

♦♦Register  of  Mines,  with  Map,  San  Diego  County 

Register  of  Mines,  with  Map,   Santa  Barbara  County — 


VIII  REPORT   OP   STATE   MINERALOGIST. 

MAPS — Continued. 

t 

Asterisks  (**)  indicate  the  publication  is  out  of  print. 

Price 

♦♦Register  of  Mines,  with  Map,  Siiasta  County  

♦♦Register  of  Mines,  with  Map,  Sierra    County    

♦♦Register  of  Mines,  with  Map,  Sisldyou  County 

♦♦Register  of  Mines,  with  Map,  Trinity    County    

♦♦Register  of  Mines,  with  Map,  Tuolumne   County    

Register  of  Mines,  with  Map,  Yuba  County 

Register  of  Oil  Wells,  with  Map,  Los  Angeles  City 

OTHER    MAPS. 

Asterisks  (**)  indicate  the  publication  is  out  of  print. 

**Map  of  California.  Showing  Mineral  Deposits   (50x60  in.)  — 
Map  of  Forest  Reserves  in  California — 

.  Mounted    ?0.50 

♦♦Unmounted    

♦*Mlneral  and  Relief  Map  of  California 

♦♦Map  of  El  Dorado  County,   Showing  Boundaries,  National  Forests 

♦♦Map  of  Madei*a  County,  Showing  Boundaries,  National  Forests 

♦♦Map  of  Placer   County,   Showing  Boundaries,   National  Forests 

♦♦Map  of  Shasta  County,   Showing  Boundaries,   National  Forests 

♦♦Map  of  Sierra  County,  Showing  Boundaries,  National  Forests 

♦♦Map  of  Siskiyou  County,  Showing  Boundaries,  National  Forests 

♦♦Map  of  Tuolumne  County,   Showing  Boundaries,  National  Forests 

♦♦Map  of  Mother   Lode    Region 

♦♦Map  of  Desert  Region  of  Southern  California 

Map  of  Minaret   District,   Madera    County .20 

AL^p  of  Copper  Deposits  in  California .05 

♦♦Map  of  Calaveras  County   

**Map  of  Plumas  County .25 

♦♦Map  of  Trinity   County   

Map  of  Tuolumne  County    .25 

Geological  Map  of  Inyo  County.     Scale  1  inch  equals  4  miles .60 

Map  of  California  accompanying  Bulletin  No.  89,  showing  generalized  classi- 
fication  of   land  with   regard   to  oil   possibilities.     Map   only,   without 

Bulletin    .25 

Geological  Map  of  California,  1910.  Scale  1  inch  equals  12  miles.  As 
accurate  and  up-to-date  as  available  data  will  permit  as  regards  topog- 
raphy and  geography.  Shows  railroads,  highways,  post  oflSces  and  other 
towns.  First  geological  map  that  has  been  available  since  1892,  and 
shows  geology  of  entire  state  as  no  other  map  does.     Geological  details 

lithographed  in  2.3  colors.     Mounted 2.50 

Topographic   Map   of    Sierra   Nevada   Gold   Belt,    showing   distribution    of 

auriferous  gravels.     In  4  colors .50 

OIL    FIELD    MAPS. 

These    maps    are    revised    from    time    to    time    as    development    work 
advances  and  ownerships  change. 

Map  No.     1 — Sargent,  Santa  Clara  County .50 

Map  No.     2 — Santa  Maria,  including  Cat  Canyon  and  Los  Alamos .75 

Map  No.     3 — Santa  Maria,  including  Casmalia  and  Lompoc .75 

Map  No.     4 — Whittier-Fullerton,    including    Olinda,    Brea    Canyon,    Puente 

Hills,  East  Coyote  and  Richfield .75 

Map  No.     5 — Whittier-Fullerton,     including     Whittier,     West     Coyote,     and 

Montebello .75 

Map  No.     6 — Salt  Lake,  Los  Angeles  County .75 

Map  No.     7 — Sunset  and  San  Emido  and  Kern  County .75 

Map  No.     8 — South  Midway  and  Buena  Vista  Hills,  Kern  County .75 

Map  No.     9 — North  Midway  and  McKittrick,  Kern  County .75 

Map  No.  10 — Belridge  and  McKittrick,  Kern  County .75 

Map  No.  11 — Lost  Hills  and  North  Belridge,  Kern  County .75 

Map  No.  12 — Devils   Den,  Kern  County .75 


FUIREAIT    IMPLICATIONS. 


IX 


OIL   FIELD    MAPS— Continued. 

Price 

Map  No.  13 — Kern  Rivor,  Kern  County $0.75 

Mop  No.  14 — Coalinsa,  Fresno  County 1.00 

Map  No.   lo — Elk  Hills.  Kern  County .75 

Map  No.   10 — Ventura-Ojai,   Ventura  County .75 

Map  No.  17 — Santa  Paiila-Sespe  Oil  Fields.  Ventura  County .75 

.Map  No.  18— PiruSinii-Newhall   Oil    Fields .75 

.Map  No.  10 — Arroyo  Grande,  San  Luis  Obispo  County .75 

.Map   No.  20— I.ong  Beach   Oil    Field 1.00 

Map  No.  21 — Portion  of  District  4,  Showing  Boundaries  of  Oil  Fields,  Kern 

and   Kings  counties ,75 

.Map  No.  22 — Portion    of    District    3.    Showing    Oil    Fields,    Santa    Barbara 

County    ,75 

.Mai)  No.  2.'^ — Portion    of    District    2,    Showing    Boundaries    of    Oil    Fields, 

Ventura  County  .75 

.Map   No.  24 — Portion  of  District  1,   Showing  Boundaries  of  Oil  Fields,  Los 

Angeles  and   Orange  counties .75 

.Map  No.  20- Huntington  Beach  Oil  Field .75 

.Map  No.  27- Santa   Fe  Springs  Oil   Field .75 

.Map  No.  2S — Torrance.  Los  Angeles  County '. .75 

Map  No.  29 — Dominguez,    Los    Angeles    County 1.00 

Map  No.  30 — Rosecrans,   Los  Angeles  County 1.00 

DETERMINATION    OF    MINERAL    SAMPLES. 

Samples  (limited  to  three  at  one  time)  of  any  mineral  found  in  the  state  may  be 
sent  to  the  Bureau  for  identification,  and  the  same  will  be  classified  free  of  charge. 
No  samples  will  be  determined  if  received  from  points  outside  the  state.  It  must  be 
understood  that  no  assays,  or  quantitative  determinations  will  be  made.  Samples 
should  be  in  lump  form  if  possible,  and  marked  plainly  with  name  of  sender  on 
outside  of  package,  etc.  No  samples  will  be  received  unless  delivery  charges  are 
prepaid.  .\  letter  should  accompany  sample,  giving  locality  where  mineral  was  found 
and    the    n.iture   of   the    information    desired. 


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MAR  1  51982 

PHYS  SCI  UBRAR^ 

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J  UN     9  1982 


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PHYS  SCI  LIBRARY 

Book  Slip-15m-8,'52(A2573s4)458 


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"AP   OF    PART   OF 

SURVEYED  AMD  UMSURVEYED  CLAIMS 
IN  THE  VICINITY  OF  RANDSBURG 

KERH  AMD    SAt-i  BERTIARDIHO  COUTTIES 
CALIFORHIA 

COMPILED       Br      O.  CLI^VEL-^m)    T/aTjOK-. 

SCALE 


MINKS   AND   PROSPECTS. 

I.  BALTIC  (OLD  SHAFT). 
1!.  BALTIC  (.NEW  SlIAPT). 
:i  BELCHEH   EX, 

4,  BEN   HUR. 
a.  BEN   HUR  EX. 
G.  BEVIS  DIVIDE. 
7.  BIG  rOUR. 

5.  BIG  SIX. 
:l  BLACK  HAWK. 

111.  BRAY   &    BISBEE. 

II.  BDLLY   BOY. 

12.  BUTTE. 

13.  CAL.  RAND  No.  1. 

14.  CAL.  RAND  No.  2. 
l.'i  CAL.  RAND  No.  6, 
It;.  CHICKEN  HAWK. 

17.  CLMA    BIMETALLIC. 

18.  CONSOLIDATED. 

19.  COYOTE. 

20.  COYOTE  No  2, 

21.  ELDER  *   IIL'STAVE   LEASB. 

22.  FLAT  TIRE. 
■13.  FOX  LEASE. 

24.  FOX  No.  2. 

25.  GARFOBD   LEASE. 

26.  GIMLET. 

27.  GOLD  COIN. 

28.  GOOD   MORNING. 

29.  GRADY  EX. 
3(1.  JOBURO  DIVIDE, 
ai.  KELLY  BAND  EX. 

32.  KENYON. 

33.  KING  SOLOMON. 

34.  LA  CROSSE. 

35.  LITTLE  BUTTE, 

36.  LITTLE  JACK. 

37.  MISPAH  MONTANA. 

38.  MISPAH  NEVADA. 
3(1.  5I0NARCU  BAND. 

40.  NANCY   HANKS. 

41.  NAVAJO. 

42.  (IXEV  LEASE 

43.  PITTSBURG  4  MT.   SHASTA. 

44.  RAND   MOUNTAIN. 

45.  RATCLnrPE  TUNGSTEN. 
411,  SANTA  FE, 
47  SILVER  BASIN. 
4H,  SILVER    BELL, 

49,  SILVER   GLANCE    LEASE. 

50.  SILVER  HOKDE  LEASE. 
.'.I.  SILVER  KINO. 
.52,  SILVER  MOON. 

53.  ST.  LAWRENCE   RAND. 

54.  SUNSHINE, 

55.  SWASTIKA. 

56.  THIRTEEN   LEASE. 

57.  TREASURE  HILL. 
.58.  WEDGE. 

59.  WHITE   HORSE   RAND 

60,  YELLOW   ASTER 


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PLATE  3 

■ACCOMPANYING  BULLFnN  95 -CALIFORNIA  STATE  MINING  BLIREAU 


